From: Sean Christopherson <seanjc@google.com>
To: Vipin Sharma <vipinsh@google.com>
Cc: pbonzini@redhat.com, bgardon@google.com, dmatlack@google.com,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [Patch v3 4/7] KVM: x86/mmu: Optimize SPTE change for aging gfn range
Date: Mon, 20 Mar 2023 17:51:43 -0700 [thread overview]
Message-ID: <ZBj/n3g/c0iqQAUj@google.com> (raw)
In-Reply-To: <20230211014626.3659152-5-vipinsh@google.com>
On Fri, Feb 10, 2023, Vipin Sharma wrote:
> } else {
> + new_spte = mark_spte_for_access_track(iter->old_spte);
> + iter->old_spte = kvm_tdp_mmu_write_spte(iter->sptep,
> + iter->old_spte, new_spte,
> + iter->level);
> /*
> * Capture the dirty status of the page, so that it doesn't get
> * lost when the SPTE is marked for access tracking.
> */
> - if (is_writable_pte(new_spte))
> - kvm_set_pfn_dirty(spte_to_pfn(new_spte));
> -
> - new_spte = mark_spte_for_access_track(new_spte);
> + if (is_writable_pte(iter->old_spte))
> + kvm_set_pfn_dirty(spte_to_pfn(iter->old_spte));
Moving this block below kvm_tdp_mmu_write_spte() is an unrelated change. Much to
my chagrin, I discovered that past me gave you this code. I still think the change
is correct, but I dropped it for now, mostly because the legacy/shadow MMU has the
same pattern (marks the PFN dirty before setting the SPTE).
I think this might actually be a bug fix, e.g. if the XCHG races with a fast page
fault fix and drops the Writable bit, the CPU could insert writable entry into the
TLB without KVM invoking kvm_set_pfn_dirty(). But I'm not 100% confident that I'm
not missing something, and _if_ there's a bug then mmu_spte_age() needs the same
fix, so for now, I dropped it.
next prev parent reply other threads:[~2023-03-21 0:51 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-11 1:46 [Patch v3 0/7] Optimize clear dirty log Vipin Sharma
2023-02-11 1:46 ` [Patch v3 1/7] KVM: x86/mmu: Add a helper function to check if an SPTE needs atomic write Vipin Sharma
2023-02-11 1:46 ` [Patch v3 2/7] KVM: x86/mmu: Atomically clear SPTE dirty state in the clear-dirty-log flow Vipin Sharma
2023-02-15 21:12 ` David Matlack
2023-03-17 22:59 ` Sean Christopherson
2023-03-17 23:50 ` Vipin Sharma
2023-02-11 1:46 ` [Patch v3 3/7] KVM: x86/mmu: Remove "record_dirty_log" in __tdp_mmu_set_spte() Vipin Sharma
2023-02-15 21:10 ` David Matlack
2023-02-11 1:46 ` [Patch v3 4/7] KVM: x86/mmu: Optimize SPTE change for aging gfn range Vipin Sharma
2023-02-15 21:15 ` David Matlack
2023-03-21 0:51 ` Sean Christopherson [this message]
2023-02-11 1:46 ` [Patch v3 5/7] KVM: x86/mmu: Remove "record_acc_track" in __tdp_mmu_set_spte() Vipin Sharma
2023-02-22 19:31 ` David Matlack
2023-02-11 1:46 ` [Patch v3 6/7] KVM: x86/mmu: Remove handle_changed_spte_dirty_log() Vipin Sharma
2023-02-22 19:36 ` David Matlack
2023-02-11 1:46 ` [Patch v3 7/7] KVM: x86/mmu: Merge all handle_changed_pte* functions Vipin Sharma
2023-02-22 19:42 ` David Matlack
2023-03-17 22:51 ` Sean Christopherson
2023-03-17 23:48 ` Vipin Sharma
2023-03-17 22:57 ` [Patch v3 0/7] Optimize clear dirty log Sean Christopherson
2023-03-17 23:51 ` Vipin Sharma
2023-03-21 0:41 ` Sean Christopherson
2023-03-21 18:11 ` Vipin Sharma
2023-03-21 19:57 ` Sean Christopherson
2023-03-21 20:40 ` Sean Christopherson
2023-03-21 21:38 ` Sean Christopherson
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