linux-kernel - Re: [PATCH v3] KVM: x86: Preserve TDP MMU roots until they are explicitly invalidated

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <168254947739.3087722.95836523643262635.b4-ty@google.com>
Date:   Wed, 26 Apr 2023 15:57:45 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>,
        Ben Gardon <bgardon@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v3] KVM: x86: Preserve TDP MMU roots until they are
 explicitly invalidated

On Wed, 26 Apr 2023 15:03:23 -0700, Sean Christopherson wrote:
> Preserve TDP MMU roots until they are explicitly invalidated by gifting
> the TDP MMU itself a reference to a root when it is allocated.  Keeping a
> reference in the TDP MMU fixes a flaw where the TDP MMU exhibits terrible
> performance, and can potentially even soft-hang a vCPU, if a vCPU
> frequently unloads its roots, e.g. when KVM is emulating SMI+RSM.
> 
> When KVM emulates something that invalidates _all_ TLB entries, e.g. SMI
> and RSM, KVM unloads all of the vCPUs roots (KVM keeps a small per-vCPU
> cache of previous roots).  Unloading roots is a simple way to ensure KVM
> flushes and synchronizes all roots for the vCPU, as KVM flushes and syncs
> when allocating a "new" root (from the vCPU's perspective).
> 
> [...]

Applied to kvm-x86 mmu to replace v2.  Same spiel as v2: pushed immediately to get
testing in -next, will squash trivialities as needed.

[1/1] KVM: x86: Preserve TDP MMU roots until they are explicitly invalidated
      https://github.com/kvm-x86/linux/commit/edbdb43fc96b

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes