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SubjectRe: [PATCH] KVM: x86: Manually flush collapsible SPTEs only when toggling flags
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On 11/09/19 21:19, Sean Christopherson wrote:
> Zapping collapsible sptes, a.k.a. 4k sptes that can be promoted into a
> large page, is only necessary when changing only the dirty logging flag
> of a memory region. If the memslot is also being moved, then all sptes
> for the memslot are zapped when it is invalidated. When a memslot is
> being created, it is impossible for there to be existing dirty mappings,
> e.g. KVM can have MMIO sptes, but not present, and thus dirty, sptes.
>
> Note, the comment and logic are shamelessly borrowed from MIPS's version
> of kvm_arch_commit_memory_region().
>
> Fixes: 3ea3b7fa9af06 ("kvm: mmu: lazy collapse small sptes into large sptes")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/x86.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b4cfd786d0b6..70e82e8f5c41 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9635,8 +9635,13 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
> * Scan sptes if dirty logging has been stopped, dropping those
> * which can be collapsed into a single large-page spte. Later
> * page faults will create the large-page sptes.
> + *
> + * There is no need to do this in any of the following cases:
> + * CREATE: No dirty mappings will already exist.
> + * MOVE/DELETE: The old mappings will already have been cleaned up by
> + * kvm_arch_flush_shadow_memslot()
> */
> - if ((change != KVM_MR_DELETE) &&
> + if (change == KVM_MR_FLAGS_ONLY &&
> (old->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
> !(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
> kvm_mmu_zap_collapsible_sptes(kvm, new);
>

Queued, thanks.

Paolo

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