lkml.org 
[lkml]   [2008]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    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


    \
     
     \ /
      Last update: 2008-07-22 06:55    [W:0.024 / U:29.736 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site