From: Paolo Bonzini <pbonzini@redhat.com>
To: KarimAllah Ahmed <karahmed@amazon.de>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: "Radim Krčmář" <rkrcmar@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
x86@kernel.org
Subject: Re: [PATCH] X86/KVM: Do not allow DISABLE_EXITS_MWAIT when LAPIC ARAT is not available
Date: Wed, 11 Apr 2018 11:26:42 +0200 [thread overview]
Message-ID: <eaf03d34-a85a-7e54-31f4-fa85fce1901e@redhat.com> (raw)
In-Reply-To: <1523438163-768-1-git-send-email-karahmed@amazon.de>
On 11/04/2018 11:16, KarimAllah Ahmed wrote:
> If the processor does not have an "Always Running APIC Timer" (aka ARAT),
> we should not give guests direct access to MWAIT. The LAPIC timer would
> stop ticking in deep C-states, so any host deadlines would not wakeup the
> host kernel.
>
> The host kernel intel_idle driver handles this by switching to broadcast
> mode when ARAT is not available and MWAIT is issued with a deep C-state
> that would stop the LAPIC timer. When MWAIT is passed through, we can not
> tell when MWAIT is issued.
>
> So just disable this capability when LAPIC ARAT is not available. I am not
> even sure if there are any CPUs with VMX support but no LAPIC ARAT or not.
The alternative would be to remove ARAT from __do_cpuid_ent when the
host lacks it and userspace has requested direct access to MWAIT.
However, this is simpler.
Queued, thanks.
Paolo
next prev parent reply other threads:[~2018-04-11 9:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-11 9:16 KarimAllah Ahmed
2018-04-11 9:26 ` Paolo Bonzini [this message]
2018-04-11 14:02 ` Sean Christopherson
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