Re: [PATCH v7 2/6] x86/mce: relocate set{clear}_mce_nospec() functions

[Dan Williams]

I notice that none of the folks from "X86 MM" are on the cc, added.

On Tue, Apr 5, 2022 at 12:49 PM Jane Chu <jane.chu@xxxxxxxxxx> wrote:
>
> Relocate the twin mce functions to arch/x86/mm/pat/set_memory.c
> file where they belong.
>
> Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
> ---
>  arch/x86/include/asm/set_memory.h | 52 -------------------------------
>  arch/x86/mm/pat/set_memory.c      | 47 ++++++++++++++++++++++++++++
>  include/linux/set_memory.h        |  9 +++---
>  3 files changed, 52 insertions(+), 56 deletions(-)
>
> diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
> index 78ca53512486..b45c4d27fd46 100644
> --- a/arch/x86/include/asm/set_memory.h
> +++ b/arch/x86/include/asm/set_memory.h
> @@ -86,56 +86,4 @@ bool kernel_page_present(struct page *page);
>
>  extern int kernel_set_to_readonly;
>
> -#ifdef CONFIG_X86_64
> -/*
> - * Prevent speculative access to the page by either unmapping
> - * it (if we do not require access to any part of the page) or
> - * marking it uncacheable (if we want to try to retrieve data
> - * from non-poisoned lines in the page).
> - */
> -static inline int set_mce_nospec(unsigned long pfn, bool unmap)
> -{
> -       unsigned long decoy_addr;
> -       int rc;
> -
> -       /* SGX pages are not in the 1:1 map */
> -       if (arch_is_platform_page(pfn << PAGE_SHIFT))
> -               return 0;
> -       /*
> -        * We would like to just call:
> -        *      set_memory_XX((unsigned long)pfn_to_kaddr(pfn), 1);
> -        * but doing that would radically increase the odds of a
> -        * speculative access to the poison page because we'd have
> -        * the virtual address of the kernel 1:1 mapping sitting
> -        * around in registers.
> -        * Instead we get tricky.  We create a non-canonical address
> -        * that looks just like the one we want, but has bit 63 flipped.
> -        * This relies on set_memory_XX() properly sanitizing any __pa()
> -        * results with __PHYSICAL_MASK or PTE_PFN_MASK.
> -        */
> -       decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63));
> -
> -       if (unmap)
> -               rc = set_memory_np(decoy_addr, 1);
> -       else
> -               rc = set_memory_uc(decoy_addr, 1);
> -       if (rc)
> -               pr_warn("Could not invalidate pfn=0x%lx from 1:1 map\n", pfn);
> -       return rc;
> -}
> -#define set_mce_nospec set_mce_nospec
> -
> -/* Restore full speculative operation to the pfn. */
> -static inline int clear_mce_nospec(unsigned long pfn)
> -{
> -       return set_memory_wb((unsigned long) pfn_to_kaddr(pfn), 1);
> -}
> -#define clear_mce_nospec clear_mce_nospec
> -#else
> -/*
> - * Few people would run a 32-bit kernel on a machine that supports
> - * recoverable errors because they have too much memory to boot 32-bit.
> - */
> -#endif
> -
>  #endif /* _ASM_X86_SET_MEMORY_H */
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 38af155aaba9..93dde949f224 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -1925,6 +1925,53 @@ int set_memory_wb(unsigned long addr, int numpages)
>  }
>  EXPORT_SYMBOL(set_memory_wb);
>
> +#ifdef CONFIG_X86_64

It seems like the only X86_64 dependency in this routine is the
address bit 63 usage, so how about:

if (!IS_ENABLED(CONFIG_64BIT))
    return 0;

...and drop the ifdef?

Other than that you can add:

Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>