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 <xiaoguangr...@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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