From: Sean Christopherson <seanjc@google.com>
To: Tyler Stachecki <stachecki.tyler@gmail.com>
Cc: Leonardo Bras <leobras@redhat.com>,
Dongli Zhang <dongli.zhang@oracle.com>,
kvm@vger.kernel.org, pbonzini@redhat.com, dgilbert@redhat.com,
tglx@linutronix.de, mingo@redhat.com,
dave.hansen@linux.intel.com, bp@alien8.de,
Tyler Stachecki <tstachecki@bloomberg.net>,
stable@vger.kernel.org
Subject: Re: [PATCH] x86/kvm: Account for fpstate->user_xfeatures changes
Date: Tue, 26 Sep 2023 13:27:28 -0700 [thread overview]
Message-ID: <ZRM-sI_KSghTGXYP@google.com> (raw)
In-Reply-To: <ZRMvd7ZKT6PXDLeK@google.com>
On Tue, Sep 26, 2023, Sean Christopherson wrote:
> There's another related oddity that will be fixed by my approach, assuming the realloc
> change is also reverted (I missed that in my pasted patch). Userspace *must* do
> KVM_SET_CPUID{2} in order to load off-by-default state, whereas there is no such
> requirement for on-by-default state.
Scratch that, KVM explicitly requires KVM_SET_CPUID2 to grant the guest access to
off-by-default features, e.g. so that the kernel/KVM doesn't need to context AMX
state if it's not exposed to the guest. Thankfully, that has always been true for
XFD-based features, i.e. AMX, so it's safe to keep that behavior even though it
diverges from on-by-default features.
next prev parent reply other threads:[~2023-09-26 20:27 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-14 1:00 [PATCH] x86/kvm: Account for fpstate->user_xfeatures changes Tyler Stachecki
2023-09-14 1:33 ` Tyler Stachecki
2023-09-14 7:15 ` Leonardo Bras
2023-09-14 9:11 ` Tyler Stachecki
2023-09-14 17:05 ` Dongli Zhang
2023-09-15 0:58 ` Tyler Stachecki
2023-09-15 7:41 ` Leonardo Bras
2023-09-15 12:27 ` Tyler Stachecki
2023-09-25 21:26 ` Sean Christopherson
2023-09-26 3:02 ` Tyler Stachecki
2023-09-26 16:31 ` Sean Christopherson
2023-09-26 17:31 ` Sean Christopherson
2023-09-26 19:22 ` Sean Christopherson
2023-09-26 20:27 ` Sean Christopherson [this message]
2023-09-15 7:13 ` Leonardo Bras
2023-09-15 7:11 ` Leonardo Bras
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