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 v2 2/2] x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE
Date: Tue, 13 Mar 2018 18:48:05 +0100 [thread overview]
Message-ID: <20180313174805.11825-3-vkuznets@redhat.com> (raw)
In-Reply-To: <20180313174805.11825-1-vkuznets@redhat.com>
vmx_save_host_state() is only called from kvm_arch_vcpu_ioctl_run() so
the context is pretty well defined and as we're past 'swapgs' MSR_GS_BASE
should contain kernel's GS base which we point to irq_stack_union.
Add new kernelmode_gs_base() API, irq_stack_union needs to be exported
as KVM can be build as module.
Acked-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/include/asm/processor.h | 5 +++++
arch/x86/kernel/cpu/common.c | 3 ++-
arch/x86/kvm/vmx.c | 3 ++-
3 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 1d816a3325a1..4fa4206029e3 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -407,6 +407,11 @@ union irq_stack_union {
DECLARE_PER_CPU_FIRST(union irq_stack_union, irq_stack_union) __visible;
DECLARE_INIT_PER_CPU(irq_stack_union);
+static inline unsigned long cpu_kernelmode_gs_base(int cpu)
+{
+ return (unsigned long)per_cpu(irq_stack_union.gs_base, cpu);
+}
+
DECLARE_PER_CPU(char *, irq_stack_ptr);
DECLARE_PER_CPU(unsigned int, irq_count);
extern asmlinkage void ignore_sysret(void);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 348cf4821240..4702fbd98f92 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -487,7 +487,7 @@ void load_percpu_segment(int cpu)
loadsegment(fs, __KERNEL_PERCPU);
#else
__loadsegment_simple(gs, 0);
- wrmsrl(MSR_GS_BASE, (unsigned long)per_cpu(irq_stack_union.gs_base, cpu));
+ wrmsrl(MSR_GS_BASE, cpu_kernelmode_gs_base(cpu));
#endif
load_stack_canary_segment();
}
@@ -1398,6 +1398,7 @@ __setup("clearcpuid=", setup_clearcpuid);
#ifdef CONFIG_X86_64
DEFINE_PER_CPU_FIRST(union irq_stack_union,
irq_stack_union) __aligned(PAGE_SIZE) __visible;
+EXPORT_PER_CPU_SYMBOL_GPL(irq_stack_union);
/*
* The following percpu variables are hot. Align current_task to
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 189a347f3952..49953e362e92 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2123,6 +2123,7 @@ static unsigned long segment_base(u16 selector)
static void vmx_save_host_state(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
+ int cpu = raw_smp_processor_id();
int i;
if (vmx->host_state.loaded)
@@ -2165,7 +2166,7 @@ static void vmx_save_host_state(struct kvm_vcpu *vcpu)
#ifdef CONFIG_X86_64
vmcs_writel(HOST_FS_BASE, current->thread.fsbase);
- vmcs_writel(HOST_GS_BASE, read_msr(MSR_GS_BASE));
+ vmcs_writel(HOST_GS_BASE, cpu_kernelmode_gs_base(cpu));
#else
vmcs_writel(HOST_FS_BASE, segment_base(vmx->host_state.fs_sel));
vmcs_writel(HOST_GS_BASE, segment_base(vmx->host_state.gs_sel));
--
2.14.3
next prev parent reply other threads:[~2018-03-13 17:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-13 17:48 [PATCH v2 0/2] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs Vitaly Kuznetsov
2018-03-13 17:48 ` [PATCH v2 1/2] x86/kvm/vmx: read MSR_{FS,KERNEL_GS}_BASE from current->thread Vitaly Kuznetsov
2018-03-13 17:48 ` Vitaly Kuznetsov [this message]
2018-03-14 16:12 ` [PATCH v2 0/2] x86/kvm: avoid expensive rdmsrs for FS/GS base MSRs Paolo Bonzini
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180313174805.11825-3-vkuznets@redhat.com \
--to=vkuznets@redhat.com \
--cc=hpa@zytor.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=rkrcmar@redhat.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).