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x86/kvm/vmx: avoid expensive rdmsr for MSR_GS_BASE

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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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Vitaly Kuznetsov 2018-03-13 18:48:05 +01:00 committed by Paolo Bonzini
parent 42b933b597
commit 35060ed6a1
3 changed files with 9 additions and 2 deletions
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5
arch/x86/include/asm/processor.h
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@ -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);

3
arch/x86/kernel/cpu/common.c
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@ -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

3
arch/x86/kvm/vmx.c
View File

@ -2153,6 +2153,7 @@ 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)
@ -2195,7 +2196,7 @@ 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));