From: Paolo Bonzini <pbonzini@redhat.com>
To: "Sean Christopherson" <sean.j.christopherson@intel.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: x86: Manually flush collapsible SPTEs only when toggling flags
Date: Tue, 17 Sep 2019 15:33:53 +0200 [thread overview]
Message-ID: <47331a39-7f74-661c-b248-266eec420efa@redhat.com> (raw)
In-Reply-To: <20190911191952.31126-1-sean.j.christopherson@intel.com>
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
prev parent reply other threads:[~2019-09-17 13:33 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-11 19:19 [PATCH] KVM: x86: Manually flush collapsible SPTEs only when toggling flags Sean Christopherson
2019-09-17 13:33 ` Paolo Bonzini [this message]
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