From: Paolo Bonzini <pbonzini@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, Dave Hansen <dave.hansen@intel.com>,
Chang Seok Bae <chang.seok.bae@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
Sasha Levin <sashal@kernel.org>,
kvm@vger.kernel.org, Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is enabled
Date: Fri, 21 Aug 2020 11:37:13 +0200 [thread overview]
Message-ID: <f8597183-5a14-de7c-330b-46b9bf015d0c@redhat.com> (raw)
In-Reply-To: <87r1s0gxfj.fsf@nanos.tec.linutronix.de>
On 21/08/20 11:28, Thomas Gleixner wrote:
> We all know that MSRs are slow, but as a general rule I have to make it
> entirely clear that the kernel has precedence over KVM.
I totally agree. I just don't think that it matters _in this case_,
because the kernel hardly has any reason to use TSC_AUX while in ring0.
Paolo
> If the kernel wants to use an MSR for it's own purposes then KVM has to
> deal with that and not the other way round. Preventing the kernel from
> using a facility freely is not an option ever.
>
> The insanities of KVM performance optimizations have bitten us more than
> once.
>
> For this particular case at hand I don't care much and we should just
> rip the whole RDPID thing out unconditionally. We still have zero
> numbers about the performance difference vs. LSL.
next prev parent reply other threads:[~2020-08-21 9:37 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-21 2:50 Sean Christopherson
2020-08-21 7:24 ` peterz
2020-08-21 7:44 ` Borislav Petkov
2020-08-21 7:47 ` Borislav Petkov
2020-08-21 8:09 ` Paolo Bonzini
2020-08-21 8:16 ` Borislav Petkov
2020-08-21 9:05 ` Paolo Bonzini
2020-08-21 9:22 ` Borislav Petkov
2020-08-21 9:44 ` Paolo Bonzini
2020-08-21 9:48 ` Borislav Petkov
2020-08-21 10:07 ` Paolo Bonzini
2020-08-22 16:42 ` Andy Lutomirski
2020-09-16 16:54 ` Paolo Bonzini
2020-08-21 9:28 ` Thomas Gleixner
2020-08-21 9:37 ` Paolo Bonzini [this message]
2020-08-21 19:55 ` hpa
2020-08-21 20:02 ` Peter Zijlstra
2020-08-21 8:56 ` kernel test robot
2020-08-21 10:28 ` kernel test robot
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