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From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Sean Christopherson <sean.j.christopherson@intel.com>,
	vkuznets@redhat.com
Subject: [PATCH 20/43] KVM: nVMX: Don't "put" vCPU or host state when switching VMCS
Date: Thu, 13 Jun 2019 19:03:06 +0200
Message-ID: <1560445409-17363-21-git-send-email-pbonzini@redhat.com> (raw)
In-Reply-To: <1560445409-17363-1-git-send-email-pbonzini@redhat.com>

From: Sean Christopherson <sean.j.christopherson@intel.com>

When switching between vmcs01 and vmcs02, KVM isn't actually switching
between guest and host.  If guest state is already loaded (the likely,
if not guaranteed, case), keep the guest state loaded and manually swap
the loaded_cpu_state pointer after propagating saved host state to the
new vmcs0{1,2}.

Avoiding the switch between guest and host reduces the latency of
switching between vmcs01 and vmcs02 by several hundred cycles, and
reduces the roundtrip time of a nested VM by upwards of 1000 cycles.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/vmx/nested.c | 23 +++++++++++++++++++-
 arch/x86/kvm/vmx/vmx.c    | 53 ++++++++++++++++++++++++++---------------------
 arch/x86/kvm/vmx/vmx.h    |  3 ++-
 3 files changed, 53 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 01275cbd7478..f4415756ddd5 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -248,18 +248,39 @@ static void free_nested(struct kvm_vcpu *vcpu)
 	free_loaded_vmcs(&vmx->nested.vmcs02);
 }
 
+static void vmx_sync_vmcs_host_state(struct vcpu_vmx *vmx,
+				     struct loaded_vmcs *prev)
+{
+	struct vmcs_host_state *dest, *src;
+
+	if (unlikely(!vmx->guest_state_loaded))
+		return;
+
+	src = &prev->host_state;
+	dest = &vmx->loaded_vmcs->host_state;
+
+	vmx_set_host_fs_gs(dest, src->fs_sel, src->gs_sel, src->fs_base, src->gs_base);
+	dest->ldt_sel = src->ldt_sel;
+#ifdef CONFIG_X86_64
+	dest->ds_sel = src->ds_sel;
+	dest->es_sel = src->es_sel;
+#endif
+}
+
 static void vmx_switch_vmcs(struct kvm_vcpu *vcpu, struct loaded_vmcs *vmcs)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct loaded_vmcs *prev;
 	int cpu;
 
 	if (vmx->loaded_vmcs == vmcs)
 		return;
 
 	cpu = get_cpu();
-	vmx_vcpu_put(vcpu);
+	prev = vmx->loaded_vmcs;
 	vmx->loaded_vmcs = vmcs;
 	vmx_vcpu_load(vcpu, cpu);
+	vmx_sync_vmcs_host_state(vmx, prev);
 	put_cpu();
 
 	vm_entry_controls_reset_shadow(vmx);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 40a6235bc4d8..09632b8239de 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1039,6 +1039,33 @@ static void pt_guest_exit(struct vcpu_vmx *vmx)
 	wrmsrl(MSR_IA32_RTIT_CTL, vmx->pt_desc.host.ctl);
 }
 
+void vmx_set_host_fs_gs(struct vmcs_host_state *host, u16 fs_sel, u16 gs_sel,
+			unsigned long fs_base, unsigned long gs_base)
+{
+	if (unlikely(fs_sel != host->fs_sel)) {
+		if (!(fs_sel & 7))
+			vmcs_write16(HOST_FS_SELECTOR, fs_sel);
+		else
+			vmcs_write16(HOST_FS_SELECTOR, 0);
+		host->fs_sel = fs_sel;
+	}
+	if (unlikely(gs_sel != host->gs_sel)) {
+		if (!(gs_sel & 7))
+			vmcs_write16(HOST_GS_SELECTOR, gs_sel);
+		else
+			vmcs_write16(HOST_GS_SELECTOR, 0);
+		host->gs_sel = gs_sel;
+	}
+	if (unlikely(fs_base != host->fs_base)) {
+		vmcs_writel(HOST_FS_BASE, fs_base);
+		host->fs_base = fs_base;
+	}
+	if (unlikely(gs_base != host->gs_base)) {
+		vmcs_writel(HOST_GS_BASE, gs_base);
+		host->gs_base = gs_base;
+	}
+}
+
 void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
@@ -1102,29 +1129,7 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	gs_base = segment_base(gs_sel);
 #endif
 
-	if (unlikely(fs_sel != host_state->fs_sel)) {
-		if (!(fs_sel & 7))
-			vmcs_write16(HOST_FS_SELECTOR, fs_sel);
-		else
-			vmcs_write16(HOST_FS_SELECTOR, 0);
-		host_state->fs_sel = fs_sel;
-	}
-	if (unlikely(gs_sel != host_state->gs_sel)) {
-		if (!(gs_sel & 7))
-			vmcs_write16(HOST_GS_SELECTOR, gs_sel);
-		else
-			vmcs_write16(HOST_GS_SELECTOR, 0);
-		host_state->gs_sel = gs_sel;
-	}
-	if (unlikely(fs_base != host_state->fs_base)) {
-		vmcs_writel(HOST_FS_BASE, fs_base);
-		host_state->fs_base = fs_base;
-	}
-	if (unlikely(gs_base != host_state->gs_base)) {
-		vmcs_writel(HOST_GS_BASE, gs_base);
-		host_state->gs_base = gs_base;
-	}
-
+	vmx_set_host_fs_gs(host_state, fs_sel, gs_sel, fs_base, gs_base);
 	vmx->guest_state_loaded = true;
 }
 
@@ -1314,7 +1319,7 @@ static void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
 		pi_set_sn(pi_desc);
 }
 
-void vmx_vcpu_put(struct kvm_vcpu *vcpu)
+static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	vmx_vcpu_pi_put(vcpu);
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index f35442093397..581f4039b346 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -303,11 +303,12 @@ struct kvm_vmx {
 
 bool nested_vmx_allowed(struct kvm_vcpu *vcpu);
 void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu);
-void vmx_vcpu_put(struct kvm_vcpu *vcpu);
 int allocate_vpid(void);
 void free_vpid(int vpid);
 void vmx_set_constant_host_state(struct vcpu_vmx *vmx);
 void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
+void vmx_set_host_fs_gs(struct vmcs_host_state *host, u16 fs_sel, u16 gs_sel,
+			unsigned long fs_base, unsigned long gs_base);
 int vmx_get_cpl(struct kvm_vcpu *vcpu);
 unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu);
 void vmx_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
-- 
1.8.3.1



  parent reply index

Thread overview: 53+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-13 17:02 [PATCH 00/43] VMX optimizations Paolo Bonzini
2019-06-13 17:02 ` [PATCH 01/43] KVM: VMX: Fix handling of #MC that occurs during VM-Entry Paolo Bonzini
2019-06-13 17:24   ` Jim Mattson
2019-06-13 17:02 ` [PATCH 02/43] kvm: nVMX: small cleanup in handle_exception Paolo Bonzini
2019-06-13 17:02 ` [PATCH 03/43] KVM: VMX: Read cached VM-Exit reason to detect external interrupt Paolo Bonzini
2019-06-13 17:02 ` [PATCH 04/43] KVM: VMX: Store the host kernel's IDT base in a global variable Paolo Bonzini
2019-06-13 17:02 ` [PATCH 05/43] KVM: x86: Move kvm_{before,after}_interrupt() calls to vendor code Paolo Bonzini
2019-06-13 17:02 ` [PATCH 06/43] KVM: VMX: Handle NMIs, #MCs and async #PFs in common irqs-disabled fn Paolo Bonzini
2019-06-13 17:02 ` [PATCH 07/43] KVM: nVMX: Intercept VMWRITEs to read-only shadow VMCS fields Paolo Bonzini
2019-06-13 17:02 ` [PATCH 08/43] KVM: nVMX: Intercept VMWRITEs to GUEST_{CS,SS}_AR_BYTES Paolo Bonzini
2019-06-13 17:02 ` [PATCH 09/43] KVM: nVMX: Track vmcs12 offsets for shadowed VMCS fields Paolo Bonzini
2019-06-13 17:02 ` [PATCH 10/43] KVM: nVMX: Lift sync_vmcs12() out of prepare_vmcs12() Paolo Bonzini
2019-06-13 17:02 ` [PATCH 11/43] KVM: nVMX: Use descriptive names for VMCS sync functions and flags Paolo Bonzini
2019-06-13 17:02 ` [PATCH 12/43] KVM: nVMX: Add helpers to identify shadowed VMCS fields Paolo Bonzini
2019-06-14 16:10   ` Sean Christopherson
2019-06-13 17:02 ` [PATCH 13/43] KVM: nVMX: Sync rarely accessed guest fields only when needed Paolo Bonzini
2019-06-13 17:03 ` [PATCH 14/43] KVM: nVMX: Rename prepare_vmcs02_*_full to prepare_vmcs02_*_rare Paolo Bonzini
2019-06-13 17:03 ` [PATCH 15/43] KVM: VMX: Always signal #GP on WRMSR to MSR_IA32_CR_PAT with bad value Paolo Bonzini
2019-06-13 17:03 ` [PATCH 16/43] KVM: nVMX: Always sync GUEST_BNDCFGS when it comes from vmcs01 Paolo Bonzini
     [not found]   ` <20190615221602.93C5721851@mail.kernel.org>
2019-06-15 22:40     ` Liran Alon
2019-06-13 17:03 ` [PATCH 17/43] KVM: nVMX: Write ENCLS-exiting bitmap once per vmcs02 Paolo Bonzini
2019-06-13 17:03 ` [PATCH 18/43] KVM: nVMX: Don't rewrite GUEST_PML_INDEX during nested VM-Entry Paolo Bonzini
2019-06-13 17:03 ` [PATCH 19/43] KVM: VMX: simplify vmx_prepare_switch_to_{guest,host} Paolo Bonzini
2019-06-13 17:03 ` Paolo Bonzini [this message]
2019-06-13 17:03 ` [PATCH 21/43] KVM: nVMX: Don't reread VMCS-agnostic state when switching VMCS Paolo Bonzini
2019-06-14 16:25   ` Sean Christopherson
2019-06-13 17:03 ` [PATCH 22/43] KVM: nVMX: Don't dump VMCS if virtual APIC page can't be mapped Paolo Bonzini
2019-06-17 19:17   ` Radim Krčmář
2019-06-17 20:07     ` Sean Christopherson
2019-06-18  9:43       ` Paolo Bonzini
2019-06-13 17:03 ` [PATCH 23/43] KVM: nVMX: Don't speculatively write virtual-APIC page address Paolo Bonzini
2019-06-13 17:03 ` [PATCH 24/43] KVM: nVMX: Don't speculatively write APIC-access " Paolo Bonzini
2019-06-13 17:03 ` [PATCH 25/43] KVM: nVMX: Update vmcs12 for MSR_IA32_CR_PAT when it's written Paolo Bonzini
2019-06-13 17:03 ` [PATCH 26/43] KVM: nVMX: Update vmcs12 for SYSENTER MSRs when they're written Paolo Bonzini
2019-06-13 17:03 ` [PATCH 27/43] KVM: nVMX: Update vmcs12 for MSR_IA32_DEBUGCTLMSR when it's written Paolo Bonzini
2019-06-13 17:03 ` [PATCH 28/43] KVM: nVMX: Don't update GUEST_BNDCFGS if it's clean in HV eVMCS Paolo Bonzini
2019-06-13 17:03 ` [PATCH 29/43] KVM: x86: introduce is_pae_paging Paolo Bonzini
2019-06-13 17:03 ` [PATCH 30/43] KVM: nVMX: Copy PDPTRs to/from vmcs12 only when necessary Paolo Bonzini
2019-06-13 17:03 ` [PATCH 31/43] KVM: nVMX: Use adjusted pin controls for vmcs02 Paolo Bonzini
2019-06-13 17:03 ` [PATCH 32/43] KVM: VMX: Add builder macros for shadowing controls Paolo Bonzini
2019-06-13 17:03 ` [PATCH 33/43] KVM: VMX: Shadow VMCS pin controls Paolo Bonzini
2019-06-13 17:03 ` [PATCH 34/43] KVM: VMX: Shadow VMCS primary execution controls Paolo Bonzini
2019-06-13 17:03 ` [PATCH 35/43] KVM: VMX: Shadow VMCS secondary " Paolo Bonzini
2019-06-13 17:03 ` [PATCH 36/43] KVM: nVMX: Shadow VMCS controls on a per-VMCS basis Paolo Bonzini
2019-06-13 17:03 ` [PATCH 37/43] KVM: nVMX: Don't reset VMCS controls shadow on VMCS switch Paolo Bonzini
2019-06-13 17:03 ` [PATCH 38/43] KVM: VMX: Explicitly initialize controls shadow at VMCS allocation Paolo Bonzini
2019-06-13 17:03 ` [PATCH 39/43] KVM: nVMX: Preserve last USE_MSR_BITMAPS when preparing vmcs02 Paolo Bonzini
2019-06-13 17:03 ` [PATCH 40/43] KVM: nVMX: Preset *DT exiting in vmcs02 when emulating UMIP Paolo Bonzini
2019-06-13 17:03 ` [PATCH 41/43] KVM: VMX: Drop hv_timer_armed from 'struct loaded_vmcs' Paolo Bonzini
2019-06-13 17:03 ` [PATCH 42/43] KVM: VMX: Leave preemption timer running when it's disabled Paolo Bonzini
2019-06-14 16:34   ` Sean Christopherson
2019-06-13 17:03 ` [PATCH 43/43] KVM: nVMX: shadow pin based execution controls Paolo Bonzini
2019-06-14 16:34   ` Sean Christopherson

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