Messages in this thread |  | | | Date | Wed, 13 Jun 2012 19:40:02 -0300 | | From | Marcelo Tosatti <> | | Subject | Re: [PATCH v6 6/9] KVM: MMU: fast path of handling guest page fault |
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On Tue, May 29, 2012 at 02:50:32PM +0800, Xiao Guangrong wrote: > If the the present bit of page fault error code is set, it indicates > the shadow page is populated on all levels, it means what we do is > only modify the access bit which can be done out of mmu-lock > > Currently, in order to simplify the code, we only fix the page fault > caused by write-protect on the fast path > > Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> > --- > arch/x86/kvm/mmu.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++----- > 1 files changed, 114 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 150c5ad..d6101a8 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -445,6 +445,11 @@ static bool __check_direct_spte_mmio_pf(u64 spte) > } > #endif > > +static bool spte_can_be_writable(u64 spte) > +{ > + return !(~spte & (SPTE_HOST_WRITEABLE | SPTE_MMU_WRITEABLE)); > +} > +
spte_is_locklessly_modifiable(). Its easy to confuse "spte_can_be_writable" with different things.
> static bool spte_has_volatile_bits(u64 spte) > { > if (!shadow_accessed_mask) > @@ -454,7 +459,7 @@ static bool spte_has_volatile_bits(u64 spte) > return false; > > if ((spte & shadow_accessed_mask) && > - (!is_writable_pte(spte) || (spte & shadow_dirty_mask))) > + (!spte_can_be_writable(spte) || (spte & shadow_dirty_mask))) > return false;
mmu_spte_update is handling several different cases. Please rewrite it, add a comment on top of it (or spread comments on top of each significant code line) with all cases it is handling (also recheck it regarding new EPT accessed/dirty bits code).
For one thing, if spte can be updated locklessly the update must be atomic:
if spte can be locklessly updated read-and-modify must be atomic.
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