Commit d974baa3 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Linus Torvalds

x86,kvm,vmx: Preserve CR4 across VM entry

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: default avatarAndy Lutomirski <luto@amacapital.net>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Cc: stable@vger.kernel.org
Cc: Petr Matousek <pmatouse@redhat.com>
Cc: Gleb Natapov <gleb@kernel.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2e923b02
...@@ -472,6 +472,7 @@ struct vcpu_vmx { ...@@ -472,6 +472,7 @@ struct vcpu_vmx {
int gs_ldt_reload_needed; int gs_ldt_reload_needed;
int fs_reload_needed; int fs_reload_needed;
u64 msr_host_bndcfgs; u64 msr_host_bndcfgs;
unsigned long vmcs_host_cr4; /* May not match real cr4 */
} host_state; } host_state;
struct { struct {
int vm86_active; int vm86_active;
...@@ -4267,11 +4268,16 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx) ...@@ -4267,11 +4268,16 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
u32 low32, high32; u32 low32, high32;
unsigned long tmpl; unsigned long tmpl;
struct desc_ptr dt; struct desc_ptr dt;
unsigned long cr4;
vmcs_writel(HOST_CR0, read_cr0() & ~X86_CR0_TS); /* 22.2.3 */ 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 */ 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 */ vmcs_write16(HOST_CS_SELECTOR, __KERNEL_CS); /* 22.2.4 */
#ifdef CONFIG_X86_64 #ifdef CONFIG_X86_64
/* /*
...@@ -7514,7 +7520,7 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx) ...@@ -7514,7 +7520,7 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
{ {
struct vcpu_vmx *vmx = to_vmx(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. */ /* Record the guest's net vcpu time for enforced NMI injections. */
if (unlikely(!cpu_has_virtual_nmis() && vmx->soft_vnmi_blocked)) if (unlikely(!cpu_has_virtual_nmis() && vmx->soft_vnmi_blocked))
...@@ -7540,6 +7546,12 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu) ...@@ -7540,6 +7546,12 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty)) if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty))
vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]); 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 /* When single-stepping over STI and MOV SS, we must clear the
* corresponding interruptibility bits in the guest state. Otherwise * corresponding interruptibility bits in the guest state. Otherwise
* vmentry fails as it then expects bit 14 (BS) in pending debug * vmentry fails as it then expects bit 14 (BS) in pending debug
......
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