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SubjectRe: [PATCH] x86: fix pte_flags() to only return flags, fix lguest.
Rusty Russell wrote:
> Change a15af1c9ea2750a9ff01e51615c45950bad8221b 'x86/paravirt: add
> pte_flags to just get pte flags' removed lguest's private pte_flags()
> in favor of a generic one.
>
> Unfortunately, the generic one doesn't filter out the non-flags bits:
> this results in lguest creating corrupt shadow page tables and blowing
> up host memory.
>
> Since noone is supposed to use the pfn part of pte_flags(), it seems
> safest to always do the filtering.
>

Thinking about this, I wonder if it needs to be a pv_op at all.
Generality says "yes", but there are no users which set it to anything
other than native_pte_flags. The point of it is to return the flags
as-is, without needing more complex stuff (like Xen's mfn to pfn
conversion).

In most cases, the surrounding code will be applying its own mask
anyway, so making it a simple inline will allow all the masks to get
folded together.

If a user which wants to do something other than return the bare flags,
it would be easy enough to put the pv_op back.

> Cc: Jeremy Fitzhardinge <jeremy@goop.org>
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
>
> diff -r ee1a6adad3d2 arch/x86/kernel/paravirt.c
> --- a/arch/x86/kernel/paravirt.c Mon Jul 21 12:49:25 2008 +1000
> +++ b/arch/x86/kernel/paravirt.c Tue Jul 22 14:09:33 2008 +1000
> @@ -428,7 +428,7 @@ struct pv_mmu_ops pv_mmu_ops = {
> #endif /* PAGETABLE_LEVELS >= 3 */
>
> .pte_val = native_pte_val,
> - .pte_flags = native_pte_val,
> + .pte_flags = native_pte_flags,
> .pgd_val = native_pgd_val,
>
> .make_pte = native_make_pte,
> diff -r ee1a6adad3d2 include/asm-x86/page.h
> --- a/include/asm-x86/page.h Mon Jul 21 12:49:25 2008 +1000
> +++ b/include/asm-x86/page.h Tue Jul 22 14:09:33 2008 +1000
> @@ -144,6 +144,18 @@ static inline pteval_t native_pte_val(pt
> return pte.pte;
> }
>
> +/* This belongs in pgtable.h, but our includes are too much of a mess. */
> +#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
> +#define PTE_FLAGS _AC(0x8000000000000FFF, ULL)
> +#else
> +#define PTE_FLAGS 0x00000FFF
> +#endif
>
We already have this, it's called PTE_MASK.

J


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