On Thu, Jun 30, 2022 at 11:37:15PM +1200, Kai Huang <kai.huang@xxxxxxxxx> wrote: > On Mon, 2022-06-27 at 14:53 -0700, isaku.yamahata@xxxxxxxxx wrote: > > From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> > > > > Explicitly check for an MMIO spte in the fast page fault flow. TDX will > > use a not-present entry for MMIO sptes, which can be mistaken for an > > access-tracked spte since both have SPTE_SPECIAL_MASK set. > > SPTE_SPECIAL_MASK has been removed in latest KVM code. The changelog needs > update. It was renamed to SPTE_TDP_AD_MASK. not removed. > In fact, if I understand correctly, I don't think this changelog is correct: > The existing code doesn't check is_mmio_spte() because: > > 1) If MMIO caching is enabled, MMIO fault is always handled in > handle_mmio_page_fault() before reaching here; > > 2) If MMIO caching is disabled, is_shadow_present_pte() always returns false for > MMIO spte, and is_mmio_spte() also always return false for MMIO spte, so there's > no need check here. > > "A non-present entry for MMIO spte" doesn't necessarily mean > is_shadow_present_pte() will return true for it, and there's no explanation at > all that for TDX guest a MMIO spte could reach here and is_shadow_present_pte() > returns true for it. Although it was needed, I noticed the following commit made this patch unnecessary. So I'll drop this patch. Kudos to Sean. edea7c4fc215c7ee1cc98363b016ad505cbac9f7 "KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs" -- Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
