On Thu, Jun 14, 2012 at 11:00:14AM +0800, Xiao Guangrong wrote: > On 06/14/2012 06:40 AM, Marcelo Tosatti wrote: > > > 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@xxxxxxxxxxxxxxxxxx> > >> --- > >> 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. > > > > > Yes. Will update it. > > >> 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). > > > > > Okay. > > > 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. > > > Actually, i did it in the v5, Avi has some comments on that. Please > see https://lkml.org/lkml/2012/5/24/55 > > What the reason we should locklessly update spte here? So far i know > is for volatile bit lost and getting a stable is_writable_spte()? Yes. > But this two cases can be avoided by using spte_can_be_writable(spte) > instead of is_writable_pte(spte), right? Well, yes, but it becomes confusing: this optimization is always going to consider sptes that can be locklessly updated as dirty, even though they are read-only. Is that what is wanted? Ok, if you/Avi want to avoid an atomic read-and-update, please introduce it later an as optimization patch. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html