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authorAndy Lutomirski <luto@amacapital.net>2014-10-08 09:02:13 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-02-11 14:48:18 +0800
commit747a43ad696d6112d99d68c8462e4ddab0b7bab2 (patch)
tree18af22ed71ab55095233d395fb5ebf0d9771d21d /arch
parentf9e5b0ded4be49805adcceff46c1f44137773b24 (diff)
downloadlinux-linaro-stable-747a43ad696d6112d99d68c8462e4ddab0b7bab2.tar.gz
x86,kvm,vmx: Preserve CR4 across VM entry
commit d974baa398f34393db76be45f7d4d04fbdbb4a0a upstream. CR4 isn't constant; at least the TSD and PCE bits can vary. TBH, treating CR0 and CR3 as constant scares me a bit, too, but it looks like it's correct. This adds a branch and a read from cr4 to each vm entry. Because it is extremely likely that consecutive entries into the same vcpu will have the same host cr4 value, this fixes up the vmcs instead of restoring cr4 after the fact. A subsequent patch will add a kernel-wide cr4 shadow, reducing the overhead in the common case to just two memory reads and a branch. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Acked-by: Paolo Bonzini <pbonzini@redhat.com> Cc: Petr Matousek <pmatouse@redhat.com> Cc: Gleb Natapov <gleb@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> [wangkai: Backport to 3.10: adjust context] Signed-off-by: Wang Kai <morgan.wang@huawei.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kvm/vmx.c16
1 files changed, 14 insertions, 2 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index b8a0ae75619f..04cc2fa7744f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -438,6 +438,7 @@ struct vcpu_vmx {
#endif
int gs_ldt_reload_needed;
int fs_reload_needed;
+ unsigned long vmcs_host_cr4; /* May not match real cr4 */
} host_state;
struct {
int vm86_active;
@@ -4076,11 +4077,16 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
u32 low32, high32;
unsigned long tmpl;
struct desc_ptr dt;
+ unsigned long cr4;
vmcs_writel(HOST_CR0, read_cr0() & ~X86_CR0_TS); /* 22.2.3 */
- vmcs_writel(HOST_CR4, read_cr4()); /* 22.2.3, 22.2.5 */
vmcs_writel(HOST_CR3, read_cr3()); /* 22.2.3 FIXME: shadow tables */
+ /* Save the most likely value for this task's CR4 in the VMCS. */
+ cr4 = read_cr4();
+ vmcs_writel(HOST_CR4, cr4); /* 22.2.3, 22.2.5 */
+ vmx->host_state.vmcs_host_cr4 = cr4;
+
vmcs_write16(HOST_CS_SELECTOR, __KERNEL_CS); /* 22.2.4 */
#ifdef CONFIG_X86_64
/*
@@ -6971,7 +6977,7 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
- unsigned long debugctlmsr;
+ unsigned long debugctlmsr, cr4;
/* Record the guest's net vcpu time for enforced NMI injections. */
if (unlikely(!cpu_has_virtual_nmis() && vmx->soft_vnmi_blocked))
@@ -6992,6 +6998,12 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty))
vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
+ cr4 = read_cr4();
+ if (unlikely(cr4 != vmx->host_state.vmcs_host_cr4)) {
+ vmcs_writel(HOST_CR4, cr4);
+ vmx->host_state.vmcs_host_cr4 = cr4;
+ }
+
/* When single-stepping over STI and MOV SS, we must clear the
* corresponding interruptibility bits in the guest state. Otherwise
* vmentry fails as it then expects bit 14 (BS) in pending debug