From: Paolo Bonzini <pbonzini@redhat.com>
To: Jim Mattson <jmattson@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>,
Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [PATCH 4/5] KVM: vmx: implement MSR_IA32_TSX_CTRL disable RTM functionality
Date: Wed, 20 Nov 2019 13:21:35 +0100 [thread overview]
Message-ID: <656c0af1-6c56-8a08-ff86-745409f6968c@redhat.com> (raw)
In-Reply-To: <CALMp9eQ=QXD5sFCADtFY0Bc9wWcn2nhq7XdahD-g4DBSgARYJw@mail.gmail.com>
On 19/11/19 22:06, Jim Mattson wrote:
>> + switch (index) {
>> + case MSR_IA32_TSX_CTRL:
>> + /* No need to pass TSX_CTRL_CPUID_CLEAR through. */
>> + vmx->guest_msrs[j].mask = ~(u64)TSX_CTRL_CPUID_CLEAR;
>> + break;
> Why even bother with the special case here? Does this make the wrmsr faster?
>
No, but it can avoid the wrmsr altogether if the guest uses the same
DISABLE_RTM setting but a different value for CPUID_CLEAR.
More important, while I am confident re-enabling TSX while in the kernel
and only restoring MSR_IA32_TSX_CTRL on return to userspace, I'm more
wary of changing CPUID bits while the kernel is running. I will update
the comment.
Paolo
next prev parent reply other threads:[~2019-11-20 12:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-18 18:17 [PATCH 0/5] KVM: vmx: implement MSR_IA32_TSX_CTRL for guests Paolo Bonzini
2019-11-18 18:17 ` [PATCH 1/5] KVM: x86: fix presentation of TSX feature in ARCH_CAPABILITIES Paolo Bonzini
2019-11-18 19:39 ` Jim Mattson
2019-11-18 20:48 ` Jim Mattson
2019-11-22 20:15 ` Sean Christopherson
2019-11-18 18:17 ` [PATCH 2/5] KVM: x86: do not modify masked bits of shared MSRs Paolo Bonzini
2019-11-19 19:00 ` Jim Mattson
2019-11-18 18:17 ` [PATCH 3/5] KVM: x86: implement MSR_IA32_TSX_CTRL effect on CPUID Paolo Bonzini
2019-11-19 20:02 ` Jim Mattson
2019-11-18 18:17 ` [PATCH 4/5] KVM: vmx: implement MSR_IA32_TSX_CTRL disable RTM functionality Paolo Bonzini
2019-11-19 21:06 ` Jim Mattson
2019-11-20 12:21 ` Paolo Bonzini [this message]
2019-12-04 23:49 ` Jim Mattson
2019-12-05 10:16 ` Paolo Bonzini
2019-11-18 18:17 ` [PATCH 5/5] KVM: vmx: use MSR_IA32_TSX_CTRL to hard-disable TSX on guest that lack it Paolo Bonzini
2019-11-21 2:22 ` Eduardo Habkost
2019-11-21 9:05 ` Paolo Bonzini
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