VMCS12 fields that are not handled through shadow VMCS are rarely
written, and thus they are also almost constant in the vmcs02. We can
thus optimize prepare_vmcs02 by skipping all the work for non-shadowed
fields in the common case.
This patch introduces the (pretty simple) tracking infrastructure; the
next patches will move work to prepare_vmcs02_full and save a few hundred
clock cycles per VMRESUME on a Haswell Xeon E5 system:
before after
cpuid 14159 13869
vmcall 15290 14951
inl_from_kernel 17703 17447
outl_to_kernel 16011 14692
self_ipi_sti_nop 16763 15825
self_ipi_tpr_sti_nop 17341 15935
wr_tsc_adjust_msr 14510 14264
rd_tsc_adjust_msr 15018 14311
mmio-wildcard-eventfd:pci-mem 16381 14947
mmio-datamatch-eventfd:pci-mem 18620 17858
portio-wildcard-eventfd:pci-io 15121 14769
portio-datamatch-eventfd:pci-io 15761 14831
(average savings 748, stdev 460).
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2ee842990976..8b6013b529b3 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -441,6 +441,7 @@ struct nested_vmx {
* data hold by vmcs12
*/
bool sync_shadow_vmcs;
+ bool dirty_vmcs12;
bool change_vmcs01_virtual_x2apic_mode;
/* L2 must run next, and mustn't decide to exit to L1. */
@@ -7879,8 +7880,10 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
{
unsigned long field;
gva_t gva;
+ struct vcpu_vmx *vmx = to_vmx(vcpu);
unsigned long exit_qualification = vmcs_readl(EXIT_QUALIFICATION);
u32 vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
+
/* The value to write might be 32 or 64 bits, depending on L1's long
* mode, and eventually we need to write that into a field of several
* possible lengths. The code below first zero-extends the value to 64
@@ -7923,6 +7926,20 @@ static int handle_vmwrite(struct kvm_vcpu *vcpu)
return kvm_skip_emulated_instruction(vcpu);
}
+ switch (field) {
+#define SHADOW_FIELD_RW(x) case x:
+#include "vmx_shadow_fields.h"
+ /*
+ * The fields that can be updated by L1 without a vmexit are
+ * always updated in the vmcs02, the others go down the slow
+ * path of prepare_vmcs02.
+ */
+ break;
+ default:
+ vmx->nested.dirty_vmcs12 = true;
+ break;
+ }
+
nested_vmx_succeed(vcpu);
return kvm_skip_emulated_instruction(vcpu);
}
@@ -7937,6 +7954,7 @@ static void set_current_vmptr(struct vcpu_vmx *vmx, gpa_t vmptr)
__pa(vmx->vmcs01.shadow_vmcs));
vmx->nested.sync_shadow_vmcs = true;
}
+ vmx->nested.dirty_vmcs12 = true;
}
/* Emulate the VMPTRLD instruction */
@@ -10569,6 +10587,11 @@ static int nested_vmx_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3, bool ne
return 0;
}
+static void prepare_vmcs02_full(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
+ bool from_vmentry)
+{
+}
+
/*
* prepare_vmcs02 is called when the L1 guest hypervisor runs its nested
* L2 guest. L1 has a vmcs for L2 (vmcs12), and this function "merges" it
@@ -10864,7 +10887,6 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
vmx_flush_tlb(vcpu, true);
}
-
}
if (enable_pml) {
@@ -10913,6 +10935,11 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
/* Note: modifies VM_ENTRY/EXIT_CONTROLS and GUEST/HOST_IA32_EFER */
vmx_set_efer(vcpu, vcpu->arch.efer);
+ if (vmx->nested.dirty_vmcs12) {
+ prepare_vmcs02_full(vcpu, vmcs12, from_vmentry);
+ vmx->nested.dirty_vmcs12 = false;
+ }
+
/* Shadow page tables on either EPT or shadow page tables. */
if (nested_vmx_load_cr3(vcpu, vmcs12->guest_cr3, nested_cpu_has_ept(vmcs12),
entry_failure_code))
--
1.8.3.1
