(drop stable from CC)

You could use git's --suppress-cc= option when sending.

On Fri, Jun 16, 2017 at 12:02:00PM -0700, Luck, Tony wrote:
> From: Tony Luck <tony.l...@intel.com>
> 
> Speculative processor accesses may reference any memory that has a
> valid page table entry.  While a speculative access won't generate
> a machine check, it will log the error in a machine check bank. That
> could cause escalation of a subsequent error since the overflow bit
> will be then set in the machine check bank status register.

...

> @@ -1056,6 +1057,40 @@ static int do_memory_failure(struct mce *m)
>       return ret;
>  }
>  
> +#ifdef CONFIG_X86_64
> +
> +void arch_unmap_kpfn(unsigned long pfn)
> +{

I guess you can move the ifdeffery inside the function.

> +     unsigned long decoy_addr;
> +
> +     /*
> +      * Unmap this page from the kernel 1:1 mappings to make sure
> +      * we don't log more errors because of speculative access to
> +      * the page.
> +      * We would like to just call:
> +      *      set_memory_np((unsigned long)pfn_to_kaddr(pfn), 1);
> +      * but doing that would radically increase the odds of a
> +      * speculative access to the posion 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_np() not checking whether we passed
> +      * a legal address.
> +      */
> +
> +#if PGDIR_SHIFT + 9 < 63 /* 9 because cpp doesn't grok ilog2(PTRS_PER_PGD) */

Please no side comments.

Also, explain why the build-time check. (Sign-extension going away for VA
space yadda yadda..., 5 2/3 level paging :-))

Also, I'm assuming this whole "workaround" of sorts should be Intel-only?

> +     decoy_addr = (pfn << PAGE_SHIFT) + (PAGE_OFFSET ^ BIT(63));
> +#else
> +#error "no unused virtual bit available"
> +#endif
> +
> +     if (set_memory_np(decoy_addr, 1))
> +             pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn);

WARNING: unnecessary whitespace before a quoted newline
#107: FILE: arch/x86/kernel/cpu/mcheck/mce.c:1089:
+               pr_warn("Could not invalidate pfn=0x%lx from 1:1 map \n", pfn);


-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 
(AG Nürnberg)
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