From: Sean Christopherson <seanjc@google.com>
To: Yosry Ahmed <yosry@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jim Mattson <jmattson@google.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v2 06/25] KVM: SVM: Fallback to flush everything if FLUSHBYASID is not available
Date: Wed, 22 Jul 2026 17:29:03 -0700 [thread overview]
Message-ID: <amFgT4pmhypNtgk-@google.com> (raw)
In-Reply-To: <20260616004155.1435766-7-yosry@kernel.org>
On Tue, Jun 16, 2026, Yosry Ahmed wrote:
> Currently, if FLUSHBYASID is not available when performing a TLB flush,
> the fallback is decrementing the ASID generation to trigger allocating a
> new ASID. In preparation for using a static ASID per vCPU (like VMX),
> just fallback to flushing everything if FLUSHBYASID is not available.
> This is probably worse from a performance perspective, but FLUSHBYASID
> has been around for ~15 years and it's not worth carrying the
> complexity.
>
> The fallback logic is moved within vmcb_set_flush_asid(), as more
Phrase this as a command, not a description, i.e. "Move the fallback logic into
blah blah blah...".
> callers will be added and will need the fallback as well. The only other
> current caller is from SEV code, and no CPUs support SEV but not
> FLUSHBYASID (at least according to AI).
next prev parent reply other threads:[~2026-07-23 0:29 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-16 0:41 [RFC PATCH v2 00/25] Optimize nSVM TLB flushes Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 01/25] KVM: nSVM: Flush the TLB after forcefully leaving nested Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 02/25] KVM: SVM: Passthrough the number of supported ASIDs Yosry Ahmed
2026-07-14 13:20 ` Yosry Ahmed
2026-07-14 21:28 ` Jim Mattson
2026-07-14 21:43 ` Yosry Ahmed
2026-07-14 23:41 ` Sean Christopherson
2026-07-15 6:32 ` Jim Mattson
2026-07-15 17:45 ` Yosry Ahmed
2026-07-15 18:20 ` Jim Mattson
2026-07-15 19:12 ` Yosry Ahmed
2026-07-16 23:09 ` Jim Mattson
2026-07-22 22:09 ` Sean Christopherson
2026-07-22 22:39 ` Jim Mattson
2026-07-23 0:27 ` Sean Christopherson
2026-07-23 2:46 ` Jim Mattson
2026-07-15 17:41 ` Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 03/25] KVM: VMX: Generalize VPID allocation to be vendor-neutral Yosry Ahmed
2026-07-22 22:26 ` Sean Christopherson
2026-07-22 22:36 ` Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 04/25] KVM: x86/mmu: Support specifying a minimum TLB tag Yosry Ahmed
2026-07-23 0:28 ` Sean Christopherson
2026-07-23 5:00 ` Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 05/25] KVM: SVM: Add helpers to set/clear ASID flush in VMCB Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 06/25] KVM: SVM: Fallback to flush everything if FLUSHBYASID is not available Yosry Ahmed
2026-07-23 0:29 ` Sean Christopherson [this message]
2026-06-16 0:41 ` [RFC PATCH v2 07/25] KVM: SVM: Duplicate pre-run ASID check for SEV and non-SEV guests Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 08/25] KVM: SEV: Stop using per-vCPU ASID for SEV VMs Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 09/25] KVM: SVM: Use a static ASID per vCPU Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 10/25] KVM: nSVM: Add a placeholder ASID for L2 Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 11/25] KVM: x86: hyper-v: Rename kvm_hv_vcpu_purge_flush_tlb() Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 12/25] KVM: x86: hyper-v: Allow puring all TLB flush FIFOs Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 13/25] KVM: nSVM: Flush both L1 and L2 ASIDs on KVM_REQ_TLB_FLUSH Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 14/25] KVM: nSVM: Move svm_switch_vmcb() to nested.c Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 15/25] KVM: nSVM: Call nested_svm_transition_tlb_flush() on every VMCB switch Yosry Ahmed
2026-07-23 0:42 ` Sean Christopherson
2026-07-23 5:07 ` Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 16/25] KVM: nSVM: Split nested_svm_transition_tlb_flush() into entry/exit fns Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 17/25] KVM: nSVM: Service local TLB flushes before nested transitions Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 18/25] KVM: nSVM: Handle nested TLB flush requests through TLB_CONTROL Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 19/25] KVM: nSVM: Flush the TLB if L1 changes L2's ASID in vmcb12 Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 20/25] KVM: nSVM: Do not reset TLB_CONTROL in vmcb02 on nested VM-Enter Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 21/25] KVM: x86/mmu: rename __kvm_mmu_invalidate_addr() Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 22/25] KVM: x86/mmu: Refactor kvm_mmu_invlpg() to allow skipping the gva flush Yosry Ahmed
2026-07-23 0:53 ` Sean Christopherson
2026-07-23 0:56 ` Sean Christopherson
2026-07-23 5:11 ` Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 23/25] KVM: nSVM: Flush L2's ASID when emulating INVLPGA Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 24/25] KVM: nSVM: Use different ASIDs for L1 and L2 Yosry Ahmed
2026-06-16 0:41 ` [RFC PATCH v2 25/25] DO NOT MERGE: Add nested_tlb_force_flush Yosry Ahmed
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