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

[Jane Chu]

On 4/11/2022 3:20 PM, Dan Williams wrote:
> I notice that none of the folks from "X86 MM" are on the cc, added.
> 

Noted, thanks!

> 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?

Sure.

> 
> Other than that you can add:
> 
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Thanks!
-jane