From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: kvm@vger.kernel.org, x86@kernel.org
Cc: linux-kernel@vger.kernel.org,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"Andy Lutomirski" <luto@kernel.org>
Subject: [PATCH 0/3] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs
Date: Mon, 12 Mar 2018 15:02:57 +0100 [thread overview]
Message-ID: <20180312140300.6166-1-vkuznets@redhat.com> (raw)
Changes since RFC [Andy Lutomirski]:
- Export new save_current_fsgs() API and call it before reading
current->thread.fs/gsbase
- New cpu_kernelmode_gs_base() API.
- Some comments added.
Some time ago Paolo suggested to take a look at probably unneeded expensive
rdmsrs for FS/GS base MSR in vmx_save_host_state(). This is called on every
vcpu run when we need to handle vmexit in userspace.
vmx_save_host_state() is always called in a very well defined context
(ioctl from userspace) so we may try to get the required values for FS/GS
bases from in-kernel variables and avoid expensive rdmsrs.
My debug shows we're shaving off 240 cpu cycles (E5-2603 v3).
Vitaly Kuznetsov (3):
x86/kvm/vmx: read MSR_FS_BASE from current->thread
x86/kvm/vmx: read MSR_KERNEL_GS_BASE from current->thread
x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE
arch/x86/include/asm/processor.h | 8 ++++++++
arch/x86/kernel/cpu/common.c | 3 ++-
arch/x86/kernel/process_64.c | 20 ++++++++++++++++++++
arch/x86/kvm/vmx.c | 9 ++++++---
4 files changed, 36 insertions(+), 4 deletions(-)
--
2.14.3
next reply other threads:[~2018-03-12 14:03 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-12 14:02 Vitaly Kuznetsov [this message]
2018-03-12 14:02 ` [PATCH 1/3] x86/kvm/vmx: read MSR_FS_BASE from current->thread Vitaly Kuznetsov
2018-03-12 15:34 ` Andy Lutomirski
2018-03-12 15:55 ` Vitaly Kuznetsov
2018-03-12 16:03 ` Paolo Bonzini
2018-03-12 16:13 ` Andy Lutomirski
2018-03-12 16:18 ` Paolo Bonzini
2018-03-12 17:00 ` Andy Lutomirski
2018-03-12 17:11 ` Paolo Bonzini
2018-03-13 13:20 ` Vitaly Kuznetsov
2018-03-13 13:24 ` Paolo Bonzini
2018-03-12 14:02 ` [PATCH 2/3] x86/kvm/vmx: read MSR_KERNEL_GS_BASE " Vitaly Kuznetsov
2018-03-12 14:03 ` [PATCH 3/3] x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE Vitaly Kuznetsov
2018-03-12 15:42 ` Andy Lutomirski
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