From: Peter Zijlstra <peterz@infradead.org>
To: Jon Kohler <jon@nutanix.com>
Cc: Babu Moger <babu.moger@amd.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Dave Hansen <dave.hansen@intel.com>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Tony Luck <tony.luck@intel.com>, Uros Bizjak <ubizjak@gmail.com>,
Petteri Aimonen <jpa@git.mail.kapsi.fi>,
Al Viro <viro@zeniv.linux.org.uk>,
Kan Liang <kan.liang@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@kernel.org>, Fan Yang <Fan_Yang@sjtu.edu.cn>,
Juergen Gross <jgross@suse.com>,
Benjamin Thiel <b.thiel@posteo.de>,
Dave Jiang <dave.jiang@intel.com>,
Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
Arvind Sankar <nivedita@alum.mit.edu>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v3] KVM: x86: use wrpkru directly in kvm_load_{guest|host}_xsave_state
Date: Wed, 12 May 2021 09:41:14 +0200 [thread overview]
Message-ID: <YJuGms6UnRVpP7U/@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210511170508.40034-1-jon@nutanix.com>
On Tue, May 11, 2021 at 01:05:02PM -0400, Jon Kohler wrote:
> diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
> index 8d33ad80704f..5bc4df3a4c27 100644
> --- a/arch/x86/include/asm/fpu/internal.h
> +++ b/arch/x86/include/asm/fpu/internal.h
> @@ -583,7 +583,13 @@ static inline void switch_fpu_finish(struct fpu *new_fpu)
> if (pk)
> pkru_val = pk->pkru;
> }
> - __write_pkru(pkru_val);
> +
> + /*
> + * WRPKRU is relatively expensive compared to RDPKRU.
> + * Avoid WRPKRU when it would not change the value.
> + */
> + if (pkru_val != rdpkru())
> + wrpkru(pkru_val);
Just wondering; why aren't we having that in a per-cpu variable? The
usual per-cpu MSR shadow approach avoids issuing any 'special' ops
entirely.
next prev parent reply other threads:[~2021-05-12 7:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-11 17:05 [PATCH v3] KVM: x86: use wrpkru directly in kvm_load_{guest|host}_xsave_state Jon Kohler
2021-05-11 19:08 ` Dave Hansen
2021-05-12 7:41 ` Peter Zijlstra [this message]
2021-05-12 18:33 ` Dave Hansen
[not found] ` <1bde6f22-166b-8552-e7f3-5731508182ea@kernel.org>
2021-05-17 2:58 ` Jon Kohler
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