RE: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk

From: JeeHeng Sia
Date: Thu Feb 09 2023 - 01:12:12 EST

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Hi Alex,

> -----Original Message-----
> From: Alexandre Ghiti <alex@xxxxxxxx>
> Sent: Wednesday, 8 February, 2023 8:05 PM
> To: JeeHeng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>; paul.walmsley@xxxxxxxxxx; palmer@xxxxxxxxxxx; aou@xxxxxxxxxxxxxxxxx
> Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Leyfoon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>; Mason Huo
> <mason.huo@xxxxxxxxxxxxxxxx>
> Subject: Re: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
>
> Hi Sia,
>
> On 2/8/23 05:43, JeeHeng Sia wrote:
> >
> >> -----Original Message-----
> >> From: Alexandre Ghiti <alex@xxxxxxxx>
> >> Sent: Tuesday, 7 February, 2023 11:46 PM
> >> To: JeeHeng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>; paul.walmsley@xxxxxxxxxx; palmer@xxxxxxxxxxx; aou@xxxxxxxxxxxxxxxxx
> >> Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Leyfoon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>; Mason Huo
> >> <mason.huo@xxxxxxxxxxxxxxxx>
> >> Subject: Re: [PATCH v3 4/4] RISC-V: Add arch functions to support hibernation/suspend-to-disk
> >>
> >> Hi Sia,
> >>
> >> On 1/27/23 10:10, Sia Jee Heng wrote:
> >>> Low level Arch functions were created to support hibernation.
> >>> swsusp_arch_suspend() relies code from __cpu_suspend_enter() to write
> >>> cpu state onto the stack, then calling swsusp_save() to save the memory
> >>> image.
> >>>
> >>> Arch specific hibernation header is implemented and is utilized by the
> >>> arch_hibernation_header_restore() and arch_hibernation_header_save()
> >>> functions. The arch specific hibernation header consists of satp, hartid,
> >>> and the cpu_resume address. The kernel built version is also need to be
> >>> saved into the hibernation image header to making sure only the same
> >>> kernel is restore when resume.
> >>>
> >>> swsusp_arch_resume() creates a temporary page table that covering only
> >>> the linear map. It copies the restore code to a 'safe' page, then start
> >>> to restore the memory image. Once completed, it restores the original
> >>> kernel's page table. It then calls into __hibernate_cpu_resume()
> >>> to restore the CPU context. Finally, it follows the normal hibernation
> >>> path back to the hibernation core.
> >>>
> >>> To enable hibernation/suspend to disk into RISCV, the below config
> >>> need to be enabled:
> >>> - CONFIG_ARCH_HIBERNATION_HEADER
> >>> - CONFIG_ARCH_HIBERNATION_POSSIBLE
> >>>
> >>> Signed-off-by: Sia Jee Heng <jeeheng.sia@xxxxxxxxxxxxxxxx>
> >>> Reviewed-by: Ley Foon Tan <leyfoon.tan@xxxxxxxxxxxxxxxx>
> >>> Reviewed-by: Mason Huo <mason.huo@xxxxxxxxxxxxxxxx>
> >>> ---
> >>> arch/riscv/Kconfig | 7 +
> >>> arch/riscv/include/asm/assembler.h | 20 ++
> >>> arch/riscv/include/asm/suspend.h | 21 ++
> >>> arch/riscv/kernel/Makefile | 1 +
> >>> arch/riscv/kernel/asm-offsets.c | 5 +
> >>> arch/riscv/kernel/hibernate-asm.S | 89 +++++++
> >>> arch/riscv/kernel/hibernate.c | 360 +++++++++++++++++++++++++++++
> >>> 7 files changed, 503 insertions(+)
> >>> create mode 100644 arch/riscv/kernel/hibernate-asm.S
> >>> create mode 100644 arch/riscv/kernel/hibernate.c
> >>>
> >>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> >>> index e2b656043abf..4555848a817f 100644
> >>> --- a/arch/riscv/Kconfig
> >>> +++ b/arch/riscv/Kconfig
> >>> @@ -690,6 +690,13 @@ menu "Power management options"
> >>>
> >>> source "kernel/power/Kconfig"
> >>>
> >>> +config ARCH_HIBERNATION_POSSIBLE
> >>> + def_bool y
> >>> +
> >>> +config ARCH_HIBERNATION_HEADER
> >>> + def_bool y
> >>> + depends on HIBERNATION
> >>> +
> >>> endmenu # "Power management options"
> >>>
> >>> menu "CPU Power Management"
> >>> diff --git a/arch/riscv/include/asm/assembler.h b/arch/riscv/include/asm/assembler.h
> >>> index ef1283d04b70..3de70d3e6ceb 100644
> >>> --- a/arch/riscv/include/asm/assembler.h
> >>> +++ b/arch/riscv/include/asm/assembler.h
> >>> @@ -59,4 +59,24 @@
> >>> REG_L s11, (SUSPEND_CONTEXT_REGS + PT_S11)(a0)
> >>> .endm
> >>>
> >>> +/**
> >>> + * copy_page - copy 1 page (4KB) of data from source to destination
> >>> + * @a0 - destination
> >>> + * @a1 - source
> >>> + */
> >>> + .macro copy_page a0, a1
> >>> + lui a2, 0x1
> >>> + add a2, a2, a0
> >>> +.1 :
> >>> + REG_L t0, 0(a1)
> >>> + REG_L t1, SZREG(a1)
> >>> +
> >>> + REG_S t0, 0(a0)
> >>> + REG_S t1, SZREG(a0)
> >>> +
> >>> + addi a0, a0, 2 * SZREG
> >>> + addi a1, a1, 2 * SZREG
> >>> + bne a2, a0, .1
> >>> + .endm
> >>> +
> >>> #endif /* __ASM_ASSEMBLER_H */
> >>> diff --git a/arch/riscv/include/asm/suspend.h b/arch/riscv/include/asm/suspend.h
> >>> index 75419c5ca272..db40ae433aa9 100644
> >>> --- a/arch/riscv/include/asm/suspend.h
> >>> +++ b/arch/riscv/include/asm/suspend.h
> >>> @@ -21,6 +21,12 @@ struct suspend_context {
> >>> #endif
> >>> };
> >>>
> >>> +/*
> >>> + * This parameter will be assigned to 0 during resume and will be used by
> >>> + * hibernation core for the subsequent resume sequence
> >>> + */
> >>> +extern int in_suspend;
> >>> +
> >>> /* Low-level CPU suspend entry function */
> >>> int __cpu_suspend_enter(struct suspend_context *context);
> >>>
> >>> @@ -36,4 +42,19 @@ int __cpu_resume_enter(unsigned long hartid, unsigned long context);
> >>> /* Used to save and restore the csr */
> >>> void suspend_save_csrs(struct suspend_context *context);
> >>> void suspend_restore_csrs(struct suspend_context *context);
> >>> +
> >>> +/* Low-level API to support hibernation */
> >>> +int swsusp_arch_suspend(void);
> >>> +int swsusp_arch_resume(void);
> >>> +int arch_hibernation_header_save(void *addr, unsigned int max_size);
> >>> +int arch_hibernation_header_restore(void *addr);
> >>> +int __hibernate_cpu_resume(void);
> >>> +
> >>> +/* Used to resume on the CPU we hibernated on */
> >>> +int hibernate_resume_nonboot_cpu_disable(void);
> >>> +
> >>> +/* Used to restore the hibernated image */
> >>> +asmlinkage void restore_image(unsigned long resume_satp, unsigned long satp_temp,
> >>> + unsigned long cpu_resume);
> >>> +asmlinkage int core_restore_code(void);
> >>> #endif
> >>> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> >>> index 4cf303a779ab..daab341d55e4 100644
> >>> --- a/arch/riscv/kernel/Makefile
> >>> +++ b/arch/riscv/kernel/Makefile
> >>> @@ -64,6 +64,7 @@ obj-$(CONFIG_MODULES) += module.o
> >>> obj-$(CONFIG_MODULE_SECTIONS) += module-sections.o
> >>>
> >>> obj-$(CONFIG_CPU_PM) += suspend_entry.o suspend.o
> >>> +obj-$(CONFIG_HIBERNATION) += hibernate.o hibernate-asm.o
> >>>
> >>> obj-$(CONFIG_FUNCTION_TRACER) += mcount.o ftrace.o
> >>> obj-$(CONFIG_DYNAMIC_FTRACE) += mcount-dyn.o
> >>> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> >>> index df9444397908..d6a75aac1d27 100644
> >>> --- a/arch/riscv/kernel/asm-offsets.c
> >>> +++ b/arch/riscv/kernel/asm-offsets.c
> >>> @@ -9,6 +9,7 @@
> >>> #include <linux/kbuild.h>
> >>> #include <linux/mm.h>
> >>> #include <linux/sched.h>
> >>> +#include <linux/suspend.h>
> >>> #include <asm/kvm_host.h>
> >>> #include <asm/thread_info.h>
> >>> #include <asm/ptrace.h>
> >>> @@ -116,6 +117,10 @@ void asm_offsets(void)
> >>>
> >>> OFFSET(SUSPEND_CONTEXT_REGS, suspend_context, regs);
> >>>
> >>> + OFFSET(HIBERN_PBE_ADDR, pbe, address);
> >>> + OFFSET(HIBERN_PBE_ORIG, pbe, orig_address);
> >>> + OFFSET(HIBERN_PBE_NEXT, pbe, next);
> >>> +
> >>> OFFSET(KVM_ARCH_GUEST_ZERO, kvm_vcpu_arch, guest_context.zero);
> >>> OFFSET(KVM_ARCH_GUEST_RA, kvm_vcpu_arch, guest_context.ra);
> >>> OFFSET(KVM_ARCH_GUEST_SP, kvm_vcpu_arch, guest_context.sp);
> >>> diff --git a/arch/riscv/kernel/hibernate-asm.S b/arch/riscv/kernel/hibernate-asm.S
> >>> new file mode 100644
> >>> index 000000000000..a83d534b89bd
> >>> --- /dev/null
> >>> +++ b/arch/riscv/kernel/hibernate-asm.S
> >>> @@ -0,0 +1,89 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0-only */
> >>> +/*
> >>> + * Hibernation support specific for RISCV
> >>> + *
> >>> + * Copyright (C) 2023 StarFive Technology Co., Ltd.
> >>> + *
> >>> + * Author: Jee Heng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
> >>> + */
> >>> +
> >>> +#include <asm/asm.h>
> >>> +#include <asm/asm-offsets.h>
> >>> +#include <asm/assembler.h>
> >>> +#include <asm/csr.h>
> >>> +
> >>> +#include <linux/linkage.h>
> >>> +
> >>> +/*
> >>> + * This code is executed when resume from the hibernation.
> >>> + *
> >>> + * It begins with loading the temporary page table then restores the memory image.
> >>> + * Finally branches to __hibernate_cpu_resume() to restore the state saved by
> >>> + * swsusp_arch_suspend().
> >>> + */
> >>> +
> >>> +/*
> >>> + * int __hibernate_cpu_resume(void)
> >>> + * Switch back to the hibernated image's page table prior to restore the CPU
> >>> + * context.
> >>> + *
> >>> + * Always returns 0 to the C code.
> >>> + */
> >>> +ENTRY(__hibernate_cpu_resume)
> >>> + /* switch to hibernated image's page table */
> >>> + csrw CSR_SATP, s0
> >>> + sfence.vma
> >>> +
> >>> + REG_L a0, hibernate_cpu_context
> >>> +
> >>> + /* Restore CSRs */
> >>> + restore_csr
> >>> +
> >>> + /* Restore registers (except A0 and T0-T6) */
> >>> + restore_reg
> >>> +
> >>> + /* Return zero value */
> >>> + add a0, zero, zero
> >>> +
> >>> + /* Return to C code */
> >>> + ret
> >>> +END(__hibernate_cpu_resume)
> >>> +
> >>> +/*
> >>> + * Prepare to restore the image.
> >>> + * a0: satp of saved page tables
> >>> + * a1: satp of temporary page tables
> >>> + * a2: cpu_resume
> >>> + */
> >>> +ENTRY(restore_image)
> >>> + mv s0, a0
> >>> + mv s1, a1
> >>> + mv s2, a2
> >>> + REG_L s4, restore_pblist
> >>> + REG_L a1, relocated_restore_code
> >>> +
> >>> + jalr a1
> >>> +END(restore_image)
> >>> +
> >>> +/*
> >>> + * The below code will be executed from a 'safe' page.
> >>> + * It first switches to the temporary page table, then start to copy the pages
> >>> + * back to the original memory location. Finally, it jumps to the __hibernate_cpu_resume()
> >>> + * to restore the CPU context.
> >>> + */
> >>> +ENTRY(core_restore_code)
> >>> + /* switch to temp page table */
> >>> + csrw satp, s1
> >>> + sfence.vma
> >>> +.Lcopy:
> >>> + /* The below code will restore the hibernated image. */
> >>> + REG_L a1, HIBERN_PBE_ADDR(s4)
> >>> + REG_L a0, HIBERN_PBE_ORIG(s4)
> >>> +
> >>> + copy_page a0, a1
> >>> +
> >>> + REG_L s4, HIBERN_PBE_NEXT(s4)
> >>> + bnez s4, .Lcopy
> >>> +
> >>> + jalr s2
> >>> +END(core_restore_code)
> >>> diff --git a/arch/riscv/kernel/hibernate.c b/arch/riscv/kernel/hibernate.c
> >>> new file mode 100644
> >>> index 000000000000..bf7f3c781820
> >>> --- /dev/null
> >>> +++ b/arch/riscv/kernel/hibernate.c
> >>> @@ -0,0 +1,360 @@
> >>> +// SPDX-License-Identifier: GPL-2.0-only
> >>> +/*
> >>> + * Hibernation support specific for RISCV
> >>> + *
> >>> + * Copyright (C) 2023 StarFive Technology Co., Ltd.
> >>> + *
> >>> + * Author: Jee Heng Sia <jeeheng.sia@xxxxxxxxxxxxxxxx>
> >>> + */
> >>> +
> >>> +#include <asm/barrier.h>
> >>> +#include <asm/cacheflush.h>
> >>> +#include <asm/mmu_context.h>
> >>> +#include <asm/page.h>
> >>> +#include <asm/pgtable.h>
> >>> +#include <asm/sections.h>
> >>> +#include <asm/set_memory.h>
> >>> +#include <asm/smp.h>
> >>> +#include <asm/suspend.h>
> >>> +
> >>> +#include <linux/cpu.h>
> >>> +#include <linux/memblock.h>
> >>> +#include <linux/pm.h>
> >>> +#include <linux/sched.h>
> >>> +#include <linux/suspend.h>
> >>> +#include <linux/utsname.h>
> >>> +
> >>> +/* The logical cpu number we should resume on, initialised to a non-cpu number */
> >>> +static int sleep_cpu = -EINVAL;
> >>> +
> >>> +/* CPU context to be saved */
> >>> +struct suspend_context *hibernate_cpu_context;
> >>> +
> >>> +unsigned long relocated_restore_code;
> >>> +
> >>> +/* Pointer to the temporary resume page table */
> >>> +pgd_t *resume_pg_dir;
> >>> +
> >>> +/**
> >>> + * struct arch_hibernate_hdr_invariants - container to store kernel build version
> >>> + * @uts_version: to save the build number and date so that the we are not resume with
> >>> + * a different kernel
> >>> + */
> >>> +struct arch_hibernate_hdr_invariants {
> >>> + char uts_version[__NEW_UTS_LEN + 1];
> >>> +};
> >>> +
> >>> +/**
> >>> + * struct arch_hibernate_hdr - helper parameters that help us to restore the image
> >>> + * @invariants: container to store kernel build version
> >>> + * @hartid: to make sure same boot_cpu executing the hibernate/restore code.
> >>> + * @saved_satp: original page table used by the hibernated image.
> >>> + * @restore_cpu_addr: the kernel's image address to restore the CPU context.
> >>> + */
> >>> +static struct arch_hibernate_hdr {
> >>> + struct arch_hibernate_hdr_invariants invariants;
> >>> + unsigned long hartid;
> >>> + unsigned long saved_satp;
> >>> + unsigned long restore_cpu_addr;
> >>> +} resume_hdr;
> >>> +
> >>> +static inline void arch_hdr_invariants(struct arch_hibernate_hdr_invariants *i)
> >>> +{
> >>> + memset(i, 0, sizeof(*i));
> >>> + memcpy(i->uts_version, init_utsname()->version, sizeof(i->uts_version));
> >>> +}
> >>> +
> >>> +/*
> >>> + * Check if the given pfn is in the 'nosave' section.
> >>> + */
> >>> +int pfn_is_nosave(unsigned long pfn)
> >>> +{
> >>> + unsigned long nosave_begin_pfn = sym_to_pfn(&__nosave_begin);
> >>> + unsigned long nosave_end_pfn = sym_to_pfn(&__nosave_end - 1);
> >>> +
> >>> + return ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn));
> >>> +}
> >>> +
> >>> +void notrace save_processor_state(void)
> >>> +{
> >>> + WARN_ON(num_online_cpus() != 1);
> >>> +}
> >>> +
> >>> +void notrace restore_processor_state(void)
> >>> +{
> >>> +}
> >>> +
> >>> +/*
> >>> + * Helper parameters need to be saved to the hibernation image header.
> >>> + */
> >>> +int arch_hibernation_header_save(void *addr, unsigned int max_size)
> >>> +{
> >>> + struct arch_hibernate_hdr *hdr = addr;
> >>> +
> >>> + if (max_size < sizeof(*hdr))
> >>> + return -EOVERFLOW;
> >>> +
> >>> + arch_hdr_invariants(&hdr->invariants);
> >>> +
> >>> + hdr->hartid = cpuid_to_hartid_map(sleep_cpu);
> >>> + hdr->saved_satp = csr_read(CSR_SATP);
> >>> + hdr->restore_cpu_addr = (unsigned long)__hibernate_cpu_resume;
> >>> +
> >>> + return 0;
> >>> +}
> >>> +EXPORT_SYMBOL(arch_hibernation_header_save);
> >>> +
> >>> +/*
> >>> + * Retrieve the helper parameters from the hibernation image header
> >>> + */
> >>> +int arch_hibernation_header_restore(void *addr)
> >>> +{
> >>> + struct arch_hibernate_hdr_invariants invariants;
> >>> + struct arch_hibernate_hdr *hdr = addr;
> >>> + int ret = 0;
> >>> +
> >>> + arch_hdr_invariants(&invariants);
> >>> +
> >>> + if (memcmp(&hdr->invariants, &invariants, sizeof(invariants))) {
> >>> + pr_crit("Hibernate image not generated by this kernel!\n");
> >>> + return -EINVAL;
> >>> + }
> >>> +
> >>> + sleep_cpu = riscv_hartid_to_cpuid(hdr->hartid);
> >>> + if (sleep_cpu < 0) {
> >>> + pr_crit("Hibernated on a CPU not known to this kernel!\n");
> >>> + sleep_cpu = -EINVAL;
> >>> + return -EINVAL;
> >>> + }
> >>> +
> >>> +#ifdef CONFIG_SMP
> >>> + ret = bringup_hibernate_cpu(sleep_cpu);
> >>> + if (ret) {
> >>> + sleep_cpu = -EINVAL;
> >>> + return ret;
> >>> + }
> >>> +#endif
> >>> + resume_hdr = *hdr;
> >>> +
> >>> + return ret;
> >>> +}
> >>> +EXPORT_SYMBOL(arch_hibernation_header_restore);
> >>> +
> >>> +int swsusp_arch_suspend(void)
> >>> +{
> >>> + int ret = 0;
> >>> +
> >>> + if (__cpu_suspend_enter(hibernate_cpu_context)) {
> >>> + sleep_cpu = smp_processor_id();
> >>> + suspend_save_csrs(hibernate_cpu_context);
> >>> + ret = swsusp_save();
> >>> + } else {
> >>> + suspend_restore_csrs(hibernate_cpu_context);
> >>> + flush_tlb_all();
> >>> +
> >>> + /* Invalidated Icache */
> >>> + flush_icache_all();
> >>> +
> >>> + /*
> >>> + * Tell the hibernation core that we've just restored
> >>> + * the memory
> >>> + */
> >>> + in_suspend = 0;
> >>> + sleep_cpu = -EINVAL;
> >>> + }
> >>> +
> >>> + return ret;
> >>> +}
> >>> +
> >>> +static unsigned long temp_pgtable_map_pte(pte_t *ptep, unsigned long vaddr, pgprot_t prot)
> >>> +{
> >>> + uintptr_t pte_idx = pte_index(vaddr);
> >>> +
> >>> + ptep[pte_idx] = pfn_pte(PFN_DOWN(__pa(vaddr)), prot);
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +#ifndef __PAGETABLE_PMD_FOLDED
> >>> +#define temp_pgtable_map_pgd_next(pgdp, vaddr, prot) \
> >>> + (pgtable_l5_enabled ? \
> >>> + temp_pgtable_map_p4d(pgdp, vaddr, prot) : \
> >>> + (pgtable_l4_enabled ? \
> >>> + temp_pgtable_map_pud((pud_t *)pgdp, vaddr, prot) : \
> >>> + temp_pgtable_map_pmd((pmd_t *)pgdp, vaddr, prot)))
> >>> +
> >>> +static unsigned long temp_pgtable_map_pmd(pmd_t *pmdp, unsigned long vaddr, pgprot_t prot)
> >>> +{
> >>> + uintptr_t pmd_idx = pmd_index(vaddr);
> >>> + pte_t *ptep;
> >>> +
> >>> + if (pmd_none(pmdp[pmd_idx])) {
> >>> + ptep = (pte_t *)get_safe_page(GFP_ATOMIC);
> >>> + if (!ptep)
> >>> + return -ENOMEM;
> >>> +
> >>> + memset(ptep, 0, PAGE_SIZE);
> >>> + pmdp[pmd_idx] = pfn_pmd(PFN_DOWN(__pa(ptep)), PAGE_TABLE);
> >>> + } else {
> >>> + ptep = (pte_t *)__va(PFN_PHYS(_pmd_pfn(pmdp[pmd_idx])));
> >>> + }
> >>> +
> >>> + return temp_pgtable_map_pte(ptep, vaddr, prot);
> >>> +}
> >>> +
> >>> +static unsigned long temp_pgtable_map_pud(pud_t *pudp, unsigned long vaddr, pgprot_t prot)
> >>> +{
> >>> + uintptr_t pud_index = pud_index(vaddr);
> >>> + pmd_t *pmdp;
> >>> +
> >>> + if (pud_val(pudp[pud_index]) == 0) {
> >>> + pmdp = (pmd_t *)get_safe_page(GFP_ATOMIC);
> >>> + if (!pmdp)
> >>> + return -ENOMEM;
> >>> +
> >>> + memset(pmdp, 0, PAGE_SIZE);
> >>> + pudp[pud_index] = pfn_pud(PFN_DOWN(__pa(pmdp)), PAGE_TABLE);
> >>> + } else {
> >>> + pmdp = (pmd_t *)__va(PFN_PHYS(_pud_pfn(pudp[pud_index])));
> >>> + }
> >>> +
> >>> + return temp_pgtable_map_pmd(pmdp, vaddr, prot);
> >>> +}
> >>> +
> >>> +static unsigned long temp_pgtable_map_p4d(p4d_t *p4dp, unsigned long vaddr, pgprot_t prot)
> >>> +{
> >>> + uintptr_t p4d_index = p4d_index(vaddr);
> >>> + pud_t *pudp;
> >>> +
> >>> + if (p4d_val(p4dp[p4d_index]) == 0) {
> >>> + pudp = (pud_t *)get_safe_page(GFP_ATOMIC);
> >>> + if (!pudp)
> >>> + return -ENOMEM;
> >>> +
> >>> + memset(pudp, 0, PAGE_SIZE);
> >>> + p4dp[p4d_index] = pfn_p4d(PFN_DOWN(__pa(pudp)), PAGE_TABLE);
> >>> + } else {
> >>> + pudp = (pud_t *)__va(PFN_PHYS(_p4d_pfn(p4dp[p4d_index])));
> >>> + }
> >>> +
> >>> + return temp_pgtable_map_pud(pudp, vaddr, prot);
> >>> +}
> >>> +
> >>> +#else
> >>> +#define temp_pgtable_map_pgd_next(nextp, vaddr, prot) \
> >>> + temp_pgtable_map_pte((pte_t *)nextp, vaddr, prot)
> >>> +#endif /* __PAGETABLE_PMD_FOLDED */
> >>> +
> >>> +static unsigned long temp_pgtable_map_pgd(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
> >>> +{
> >>> + uintptr_t pgd_idx = pgd_index(vaddr);
> >>> + void *nextp;
> >>> +
> >>> + if (pgd_val(pgdp[pgd_idx]) == 0) {
> >>> + nextp = (void *)get_safe_page(GFP_ATOMIC);
> >>> + if (!nextp)
> >>> + return -ENOMEM;
> >>> +
> >>> + memset(nextp, 0, PAGE_SIZE);
> >>> + pgdp[pgd_idx] = pfn_pgd(PFN_DOWN(__pa(nextp)), PAGE_TABLE);
> >>> + } else {
> >>> + nextp = (void *)__va(PFN_PHYS(_pgd_pfn(pgdp[pgd_idx])));
> >>> + }
> >>> +
> >>> + return temp_pgtable_map_pgd_next(nextp, vaddr, prot);
> >>> +}
> >>> +
> >>> +static unsigned long temp_pgtable_mapping(pgd_t *pgdp, unsigned long vaddr, pgprot_t prot)
> >>> +{
> >>> + return temp_pgtable_map_pgd(pgdp, vaddr, prot);
> >>> +}
> >>> +
> >>> +static unsigned long relocate_restore_code(void)
> >>> +{
> >>> + unsigned long ret;
> >>> + void *page = (void *)get_safe_page(GFP_ATOMIC);
> >>> +
> >>> + if (!page)
> >>> + return -ENOMEM;
> >>> +
> >>> + copy_page(page, core_restore_code);
> >>> +
> >>> + /* Make the page containing the relocated code executable */
> >>> + set_memory_x((unsigned long)page, 1);
> >>> +
> >>> + ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)page, PAGE_KERNEL_READ_EXEC);
> >>> + if (ret)
> >>> + return ret;
> >>> +
> >>> + return (unsigned long)page;
> >>> +}
> >>> +
> >>> +int swsusp_arch_resume(void)
> >>> +{
> >>> + unsigned long addr = PAGE_OFFSET;
> >>> + unsigned long ret;
> >>> +
> >>> + /*
> >>> + * Memory allocated by get_safe_page() will be dealt with by the hibernation core,
> >>> + * we don't need to free it here.
> >>> + */
> >>> + resume_pg_dir = (pgd_t *)get_safe_page(GFP_ATOMIC);
> >>> + if (!resume_pg_dir)
> >>> + return -ENOMEM;
> >>> +
> >>> + /*
> >>> + * The pages need to be writable when restoring the image.
> >>> + * Create a second copy of page table just for the linear map, and use this when
> >>> + * restoring.
> >>> + */
> >>> + for (; addr <= (unsigned long)pfn_to_virt(max_low_pfn); addr += PAGE_SIZE) {
> >>> + ret = temp_pgtable_mapping(resume_pg_dir, addr, PAGE_KERNEL);
> >>> + if (ret)
> >>> + return (int)ret;
> >>> + }
> >>> +
> >>
> >> To me this is wrong as this does not account for the real physical
> >> mapping layout: can't you simply copy the linear mapping from
> >> swapper_pg_dir?
> > Hi, we covering the linear mapping from PAGE_OFFSET up to pfn_to_virt(max_low_pfn). We shouldn't copy from the
> swapper_pg_dir as we are not suppose to modify its content.
>
>
> First, you're right, we need the temporary page table as swapper_pg_dir
> will get overwritten under our feet.
>
> Now, I still disagree with mapping all the memory: the linear mapping is
> sparse because we only map what memblock gives us (some regions are
> marked as "nomap" for a reason).
>
> I just took a look at arm64, and they do exactly that: they go through
> swapper_pg_dir, copy the linear mapping and enable write at every leaf
> level
> (https://elixir.bootlin.com/linux/latest/source/arch/arm64/kernel/hibernate.c#L419).
You're right, but we don’t have to copy from the swapper_pg_dir. We can insert kernel_page_present() to the function to check the page validity prior to do the mapping. Agree?
>
>
> >> But I have to admit that I struggle to understand the need for this
> >> temporary page table: all we need to do is to allow to write to the
> >> linear mapping, so why don't we simply set_memory_rw(linear mapping)?
> > Similar to the above comment. When we restore the memory content, we need to make sure the pages are write-able. if you modify
> the swapper_pg_dir, the kernel will crash afterwards.
> > That’s why we need a second page table to do the recovering job.
> >>
> >>> + /* Move the restore code to a new page so that it doesn't get overwritten by itself */
> >>> + relocated_restore_code = relocate_restore_code();
> >>
> >> And do we really need to do that too? The code in question can only be
> >> overwritten by the same code right?
> > Yes, we need to move the recovering code to a new page to prevent the code from overwrite itself when restoring the memory.
> >> Thanks,
> >>
> >> Alex
> >>
> >>
> >>> + if (relocated_restore_code == -ENOMEM)
> >>> + return -ENOMEM;
> >>> +
> >>> + /*
> >>> + * Map the __hibernate_cpu_resume() address to the temporary page table so that the
> >>> + * restore code can jump to it after finished restore the image. The next execution
> >>> + * code doesn't find itself in a different address space after switching over to the
> >>> + * original page table used by the hibernated image.
> >>> + */
> >>> + ret = temp_pgtable_mapping(resume_pg_dir, (unsigned long)resume_hdr.restore_cpu_addr,
> >>> + PAGE_KERNEL_READ_EXEC);
> >>> + if (ret)
> >>> + return ret;
> >>> +
> >>> + restore_image(resume_hdr.saved_satp, (PFN_DOWN(__pa(resume_pg_dir)) | satp_mode),
> >>> + resume_hdr.restore_cpu_addr);
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +#ifdef CONFIG_PM_SLEEP_SMP
> >>> +int hibernate_resume_nonboot_cpu_disable(void)
> >>> +{
> >>> + if (sleep_cpu < 0) {
> >>> + pr_err("Failing to resume from hibernate on an unknown CPU.\n");
> >>> + return -ENODEV;
> >>> + }
> >>> +
> >>> + return freeze_secondary_cpus(sleep_cpu);
> >>> +}
> >>> +#endif
> >>> +
> >>> +static int __init riscv_hibernate_init(void)
> >>> +{
> >>> + hibernate_cpu_context = kcalloc(1, sizeof(struct suspend_context), GFP_KERNEL);
> >>> +
> >>> + if (WARN_ON(!hibernate_cpu_context))
> >>> + return -ENOMEM;
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> +early_initcall(riscv_hibernate_init);
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv

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