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authorPaolo Bonzini <pbonzini@redhat.com>2014-02-21 10:32:27 +0100
committerPaolo Bonzini <pbonzini@redhat.com>2014-03-11 10:46:04 +0100
commitfacb0139698923dc7b7d15cafbb319219969f4fd (patch)
treed2f4e83b00ecfc8d744c8f8af5510bca5a8185cc
parent5315c716b69f47e1751d09e16c7bd5b559419531 (diff)
downloadop-kernel-dev-facb0139698923dc7b7d15cafbb319219969f4fd.zip
op-kernel-dev-facb0139698923dc7b7d15cafbb319219969f4fd.tar.gz
KVM: svm: Allow the guest to run with dirty debug registers
When not running in guest-debug mode (i.e. the guest controls the debug registers, having to take an exit for each DR access is a waste of time. If the guest gets into a state where each context switch causes DR to be saved and restored, this can take away as much as 40% of the execution time from the guest. If the guest is running with vcpu->arch.db == vcpu->arch.eff_db, we can let it write freely to the debug registers and reload them on the next exit. We still need to exit on the first access, so that the KVM_DEBUGREG_WONT_EXIT flag is set in switch_db_regs; after that, further accesses to the debug registers will not cause a vmexit. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--arch/x86/kvm/svm.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 86d802b..a449c3d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -34,6 +34,7 @@
#include <asm/perf_event.h>
#include <asm/tlbflush.h>
#include <asm/desc.h>
+#include <asm/debugreg.h>
#include <asm/kvm_para.h>
#include <asm/virtext.h>
@@ -1683,6 +1684,21 @@ static void svm_set_dr6(struct kvm_vcpu *vcpu, unsigned long value)
mark_dirty(svm->vmcb, VMCB_DR);
}
+static void svm_sync_dirty_debug_regs(struct kvm_vcpu *vcpu)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+
+ get_debugreg(vcpu->arch.db[0], 0);
+ get_debugreg(vcpu->arch.db[1], 1);
+ get_debugreg(vcpu->arch.db[2], 2);
+ get_debugreg(vcpu->arch.db[3], 3);
+ vcpu->arch.dr6 = svm_get_dr6(vcpu);
+ vcpu->arch.dr7 = svm->vmcb->save.dr7;
+
+ vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_WONT_EXIT;
+ set_dr_intercepts(svm);
+}
+
static void svm_set_dr7(struct kvm_vcpu *vcpu, unsigned long value)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -2974,6 +2990,17 @@ static int dr_interception(struct vcpu_svm *svm)
unsigned long val;
int err;
+ if (svm->vcpu.guest_debug == 0) {
+ /*
+ * No more DR vmexits; force a reload of the debug registers
+ * and reenter on this instruction. The next vmexit will
+ * retrieve the full state of the debug registers.
+ */
+ clr_dr_intercepts(svm);
+ svm->vcpu.arch.switch_db_regs |= KVM_DEBUGREG_WONT_EXIT;
+ return 1;
+ }
+
if (!boot_cpu_has(X86_FEATURE_DECODEASSISTS))
return emulate_on_interception(svm);
@@ -4300,6 +4327,7 @@ static struct kvm_x86_ops svm_x86_ops = {
.get_dr6 = svm_get_dr6,
.set_dr6 = svm_set_dr6,
.set_dr7 = svm_set_dr7,
+ .sync_dirty_debug_regs = svm_sync_dirty_debug_regs,
.cache_reg = svm_cache_reg,
.get_rflags = svm_get_rflags,
.set_rflags = svm_set_rflags,
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