Re: [PATCH 3/3] riscv: Make sure the kernel mapping does not overlap with IS_ERR_VALUE

From: Alex Ghiti
Date: Mon Jul 26 2021 - 01:47:23 EST


Hi Palmer,

Le 29/06/2021 à 11:13, Alexandre Ghiti a écrit :
The check that is done in setup_bootmem currently only works for 32-bit
kernel since the kernel mapping has been moved outside of the linear
mapping for 64-bit kernel. So make sure that for 64-bit kernel, the kernel
mapping does not overlap with the last 4K of the addressable memory.

Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
---
arch/riscv/mm/init.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index a1a0c4afa80f..a90c41bc9485 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -156,7 +156,7 @@ static void __init setup_bootmem(void)
{
phys_addr_t vmlinux_end = __pa_symbol(&_end);
phys_addr_t vmlinux_start = __pa_symbol(&_start);
- phys_addr_t max_mapped_addr = __pa(~(ulong)0);
+ phys_addr_t __maybe_unused max_mapped_addr;
phys_addr_t dram_end;
#ifdef CONFIG_XIP_KERNEL
@@ -179,14 +179,20 @@ static void __init setup_bootmem(void)
memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
dram_end = memblock_end_of_DRAM();
+#ifndef CONFIG_64BIT
/*
* memblock allocator is not aware of the fact that last 4K bytes of
* the addressable memory can not be mapped because of IS_ERR_VALUE
* macro. Make sure that last 4k bytes are not usable by memblock
- * if end of dram is equal to maximum addressable memory.
+ * if end of dram is equal to maximum addressable memory. For 64-bit
+ * kernel, this problem can't happen here as the end of the virtual
+ * address space is occupied by the kernel mapping then this check must
+ * be done in create_kernel_page_table.

This comment is wrong, I have just sent a patch fixing this:

"riscv: Fix comment regarding kernel mapping overlapping with IS_ERR_VALUE"

*/
+ max_mapped_addr = __pa(~(ulong)0);
if (max_mapped_addr == (dram_end - 1))
memblock_set_current_limit(max_mapped_addr - 4096);
+#endif
min_low_pfn = PFN_UP(memblock_start_of_DRAM());
max_low_pfn = max_pfn = PFN_DOWN(dram_end);
@@ -556,6 +562,7 @@ static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size,
uintptr_t va, end_va;
end_va = kernel_virt_addr + load_sz;
+

I saw that you removed this useless new line, thanks.

for (va = kernel_virt_addr; va < end_va; va += map_size)
create_pgd_mapping(pgdir, va,
load_pa + (va - kernel_virt_addr),
@@ -602,6 +609,13 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
/* Sanity check alignment and size */
BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
BUG_ON((load_pa % map_size) != 0);
+#ifdef CONFIG_64BIT
+ /*
+ * The last 4K bytes of the addressable memory can not be mapped because
+ * of IS_ERR_VALUE macro.
+ */
+ BUG_ON((kernel_virt_addr + load_sz) > ADDRESS_SPACE_END - SZ_4K);
+#endif
pt_ops.alloc_pte = alloc_pte_early;
pt_ops.get_pte_virt = get_pte_virt_early;


The merge you have done is correct to me. Sorry about the above mistakes, should have caught those before.

Thanks,

Alex