From: Sean Christopherson <seanjc@google.com>
To: Yan Zhao <yan.y.zhao@intel.com>
Cc: Like Xu <like.xu.linux@gmail.com>,
kvm@vger.kernel.org, intel-gfx@lists.freedesktop.org,
linux-kernel@vger.kernel.org,
Zhenyu Wang <zhenyuw@linux.intel.com>,
Ben Gardon <bgardon@google.com>,
Paolo Bonzini <pbonzini@redhat.com>,
intel-gvt-dev@lists.freedesktop.org,
Zhi Wang <zhi.a.wang@intel.com>
Subject: Re: [PATCH 19/27] KVM: x86/mmu: Use page-track notifiers iff there are external users
Date: Wed, 9 Aug 2023 07:33:45 -0700 [thread overview]
Message-ID: <ZNOjyf2OHQZYfMEJ@google.com> (raw)
In-Reply-To: <ZNLlseYag5DniUg3@yzhao56-desk.sh.intel.com>
On Wed, Aug 09, 2023, Yan Zhao wrote:
> On Mon, Aug 07, 2023 at 10:19:07AM -0700, Sean Christopherson wrote:
> > On Mon, Aug 07, 2023, Like Xu wrote:
> > > On 23/12/2022 8:57 am, Sean Christopherson wrote:
> > > > +static inline void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa,
> > > > + const u8 *new, int bytes)
> > > > +{
> > > > + __kvm_page_track_write(vcpu, gpa, new, bytes);
> > > > +
> > > > + kvm_mmu_track_write(vcpu, gpa, new, bytes);
> > > > +}
> > >
> > > The kvm_mmu_track_write() is only used for x86, where the incoming parameter
> > > "u8 *new" has not been required since 0e0fee5c539b ("kvm: mmu: Fix race in
> > > emulated page table writes"), please help confirm if it's still needed ? Thanks.
> > > A minor clean up is proposed.
> >
> > Hmm, unless I'm misreading things, KVMGT ultimately doesn't consume @new either.
> > So I think we can remove @new from kvm_page_track_write() entirely.
> Sorry for the late reply.
> Yes, KVMGT does not consume @new and it reads the guest PTE again in the
> page track write handler.
>
> But I have a couple of questions related to the memtioned commit as
> below:
>
> (1) If "re-reading the current value of the guest PTE after the MMU lock has
> been acquired", then should KVMGT also acquire the MMU lock too?
No. If applicable, KVMGT should read the new/current value after acquiring
whatever lock protects the generation (or update) of the shadow entries. I
suspect KVMGT already does this, but I don't have time to confirm that at this
exact memory.
The race that was fixed in KVM was:
vCPU0 vCPU1
write X
write Y
sync SPTE w/ Y
sync SPTE w/ X
Reading the value after acquiring mmu_lock ensures that both vCPUs will see whatever
value "loses" the race, i.e. whatever written value is processed second ('Y' in the
above sequence).
> If so, could we move the MMU lock and unlock into kvm_page_track_write()
> as it's common.
>
> (2) Even if KVMGT consumes @new,
> will kvm_page_track_write() be called for once or twice if there are two
> concurent emulated write?
Twice, kvm_page_track_write() is wired up directly to the emulation of the write,
i.e. there is no batching.
next prev parent reply other threads:[~2023-08-09 14:33 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-23 0:57 [PATCH 00/27] drm/i915/gvt: KVM: KVMGT fixes and page-track cleanups Sean Christopherson
2022-12-23 0:57 ` [PATCH 01/27] drm/i915/gvt: Verify pfn is "valid" before dereferencing "struct page" Sean Christopherson
2022-12-23 0:57 ` [PATCH 02/27] KVM: x86/mmu: Factor out helper to get max mapping size of a memslot Sean Christopherson
2022-12-23 0:57 ` [PATCH 03/27] drm/i915/gvt: Incorporate KVM memslot info into check for 2MiB GTT entry Sean Christopherson
2022-12-28 5:42 ` Yan Zhao
2023-01-03 21:13 ` Sean Christopherson
2023-01-05 3:07 ` Yan Zhao
2023-01-05 17:40 ` Sean Christopherson
2023-01-06 5:56 ` Yan Zhao
2023-01-06 23:01 ` Sean Christopherson
2023-01-09 9:58 ` Yan Zhao
2023-01-11 17:55 ` Sean Christopherson
2023-01-19 2:58 ` Zhenyu Wang
2023-01-19 5:26 ` Yan Zhao
2023-02-23 20:41 ` Sean Christopherson
2023-02-24 5:09 ` Yan Zhao
2023-01-12 8:31 ` Yan Zhao
2022-12-23 0:57 ` [PATCH 04/27] drm/i915/gvt: Verify VFIO-pinned page is THP when shadowing 2M gtt entry Sean Christopherson
2022-12-23 0:57 ` [PATCH 05/27] drm/i915/gvt: Put the page reference obtained by KVM's gfn_to_pfn() Sean Christopherson
2022-12-23 0:57 ` [PATCH 06/27] drm/i915/gvt: Don't rely on KVM's gfn_to_pfn() to query possible 2M GTT Sean Christopherson
2022-12-23 0:57 ` [PATCH 07/27] drm/i915/gvt: Use an "unsigned long" to iterate over memslot gfns Sean Christopherson
2022-12-23 0:57 ` [PATCH 08/27] drm/i915/gvt: Hoist acquisition of vgpu_lock out to kvmgt_page_track_write() Sean Christopherson
2022-12-23 0:57 ` [PATCH 09/27] drm/i915/gvt: Protect gfn hash table with dedicated mutex Sean Christopherson
2022-12-28 5:03 ` Yan Zhao
2023-01-03 20:43 ` Sean Christopherson
2023-01-05 0:51 ` Yan Zhao
2022-12-23 0:57 ` [PATCH 10/27] KVM: x86/mmu: Don't rely on page-track mechanism to flush on memslot change Sean Christopherson
2022-12-23 0:57 ` [PATCH 11/27] KVM: x86/mmu: Don't bounce through page-track mechanism for guest PTEs Sean Christopherson
2022-12-23 0:57 ` [PATCH 12/27] KVM: drm/i915/gvt: Drop @vcpu from KVM's ->track_write() hook Sean Christopherson
2022-12-23 0:57 ` [PATCH 13/27] KVM: x86: Reject memslot MOVE operations if KVMGT is attached Sean Christopherson
2022-12-23 0:57 ` [PATCH 14/27] drm/i915/gvt: Don't bother removing write-protection on to-be-deleted slot Sean Christopherson
2022-12-23 0:57 ` [PATCH 15/27] KVM: x86: Add a new page-track hook to handle memslot deletion Sean Christopherson
2022-12-23 0:57 ` [PATCH 16/27] drm/i915/gvt: switch from ->track_flush_slot() to ->track_remove_region() Sean Christopherson
2022-12-23 0:57 ` [PATCH 17/27] KVM: x86: Remove the unused page-track hook track_flush_slot() Sean Christopherson
2022-12-23 0:57 ` [PATCH 18/27] KVM: x86/mmu: Move KVM-only page-track declarations to internal header Sean Christopherson
2022-12-23 0:57 ` [PATCH 19/27] KVM: x86/mmu: Use page-track notifiers iff there are external users Sean Christopherson
2022-12-28 6:56 ` Yan Zhao
2023-01-04 0:50 ` Sean Christopherson
2023-08-07 12:01 ` Like Xu
2023-08-07 17:19 ` Sean Christopherson
2023-08-09 1:02 ` Yan Zhao
2023-08-09 14:33 ` Sean Christopherson [this message]
2023-08-09 23:21 ` Yan Zhao
2023-08-10 3:02 ` Yan Zhao
2023-08-10 15:41 ` Sean Christopherson
2023-08-11 5:57 ` Yan Zhao
2022-12-23 0:57 ` [PATCH 20/27] KVM: x86/mmu: Drop infrastructure for multiple page-track modes Sean Christopherson
2022-12-23 0:57 ` [PATCH 21/27] KVM: x86/mmu: Rename page-track APIs to reflect the new reality Sean Christopherson
2022-12-23 0:57 ` [PATCH 22/27] KVM: x86/mmu: Assert that correct locks are held for page write-tracking Sean Christopherson
2022-12-23 0:57 ` [PATCH 23/27] KVM: x86/mmu: Bug the VM if write-tracking is used but not enabled Sean Christopherson
2022-12-23 0:57 ` [PATCH 24/27] KVM: x86/mmu: Drop @slot param from exported/external page-track APIs Sean Christopherson
2022-12-23 0:57 ` [PATCH 25/27] KVM: x86/mmu: Handle KVM bookkeeping in page-track APIs, not callers Sean Christopherson
2022-12-23 0:57 ` [PATCH 26/27] KVM: x86/mmu: Add page-track API to query if a gfn is valid Sean Christopherson
2022-12-28 7:57 ` Yan Zhao
2023-01-03 21:19 ` Sean Christopherson
2023-01-05 3:12 ` Yan Zhao
2023-01-05 17:53 ` Sean Christopherson
2022-12-23 0:57 ` [PATCH 27/27] drm/i915/gvt: Drop final dependencies on KVM internal details Sean Christopherson
2022-12-23 9:05 ` [PATCH 00/27] drm/i915/gvt: KVM: KVMGT fixes and page-track cleanups Yan Zhao
2023-01-04 1:01 ` Sean Christopherson
2023-01-05 3:13 ` Yan Zhao
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