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From: Andy Lutomirski <luto@amacapital.net>
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Date: Wed, 8 Oct 2014 09:02:13 -0700
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Subject: [PATCH] x86,kvm,vmx: Preserve CR4 across VM entry
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CR4 isn't constant; at least the TSD and PCE bits can vary.
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TBH, treating CR0 and CR3 as constant scares me a bit, too, but it looks
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like it's correct.
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This adds a branch and a read from cr4 to each vm entry. Because it is
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extremely likely that consecutive entries into the same vcpu will have
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the same host cr4 value, this fixes up the vmcs instead of restoring cr4
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after the fact. A subsequent patch will add a kernel-wide cr4 shadow,
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reducing the overhead in the common case to just two memory reads and a
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branch.
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Signed-off-by: Andy Lutomirski <luto@amacapital.net>
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Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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Cc: stable@vger.kernel.org
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Cc: Petr Matousek <pmatouse@redhat.com>
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Cc: Gleb Natapov <gleb@kernel.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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arch/x86/kvm/vmx.c | 16 ++++++++++++++--
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1 file changed, 14 insertions(+), 2 deletions(-)
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diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
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index bfe11cf124a1..6a118fa378b5 100644
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--- a/arch/x86/kvm/vmx.c
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+++ b/arch/x86/kvm/vmx.c
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@@ -453,6 +453,7 @@ struct vcpu_vmx {
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int gs_ldt_reload_needed;
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int fs_reload_needed;
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u64 msr_host_bndcfgs;
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+ unsigned long vmcs_host_cr4; /* May not match real cr4 */
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} host_state;
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struct {
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int vm86_active;
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@@ -4235,11 +4236,16 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
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u32 low32, high32;
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unsigned long tmpl;
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struct desc_ptr dt;
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+ unsigned long cr4;
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vmcs_writel(HOST_CR0, read_cr0() & ~X86_CR0_TS); /* 22.2.3 */
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- vmcs_writel(HOST_CR4, read_cr4()); /* 22.2.3, 22.2.5 */
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vmcs_writel(HOST_CR3, read_cr3()); /* 22.2.3 FIXME: shadow tables */
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+ /* Save the most likely value for this task's CR4 in the VMCS. */
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+ cr4 = read_cr4();
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+ vmcs_writel(HOST_CR4, cr4); /* 22.2.3, 22.2.5 */
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+ vmx->host_state.vmcs_host_cr4 = cr4;
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+
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vmcs_write16(HOST_CS_SELECTOR, __KERNEL_CS); /* 22.2.4 */
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#ifdef CONFIG_X86_64
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/*
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@@ -7376,7 +7382,7 @@ static void atomic_switch_perf_msrs(struct vcpu_vmx *vmx)
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static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
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{
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struct vcpu_vmx *vmx = to_vmx(vcpu);
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- unsigned long debugctlmsr;
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+ unsigned long debugctlmsr, cr4;
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/* Record the guest's net vcpu time for enforced NMI injections. */
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if (unlikely(!cpu_has_virtual_nmis() && vmx->soft_vnmi_blocked))
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@@ -7397,6 +7403,12 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
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if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty))
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vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
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+ cr4 = read_cr4();
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+ if (unlikely(cr4 != vmx->host_state.vmcs_host_cr4)) {
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+ vmcs_writel(HOST_CR4, cr4);
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+ vmx->host_state.vmcs_host_cr4 = cr4;
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+ }
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+
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/* When single-stepping over STI and MOV SS, we must clear the
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* corresponding interruptibility bits in the guest state. Otherwise
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* vmentry fails as it then expects bit 14 (BS) in pending debug
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--
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1.9.3
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