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From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Xiaoyao Li <xiaoyao.li@intel.com>,
	Reiji Watanabe <reijiw@google.com>
Subject: [PATCH 09/15] KVM: VMX: Use flag to indicate "active" uret MSRs instead of sorting list
Date: Tue,  4 May 2021 10:17:28 -0700	[thread overview]
Message-ID: <20210504171734.1434054-10-seanjc@google.com> (raw)
In-Reply-To: <20210504171734.1434054-1-seanjc@google.com>

Explicitly flag a uret MSR as needing to be loaded into hardware instead of
resorting the list of "active" MSRs and tracking how many MSRs in total
need to be loaded.  The only benefit to sorting the list is that the loop
to load MSRs during vmx_prepare_switch_to_guest() doesn't need to iterate
over all supported uret MRS, only those that are active.  But that is a
pointless optimization, as the most common case, running a 64-bit guest,
will load the vast majority of MSRs.  Not to mention that a single WRMSR is
far more expensive than iterating over the list.

Providing a stable list order obviates the need to track a given MSR's
"slot" in the per-CPU list of user return MSRs; all lists simply use the
same ordering.  Future patches will take advantage of the stable order to
further simplify the related code.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/vmx/vmx.c | 80 ++++++++++++++++++++++--------------------
 arch/x86/kvm/vmx/vmx.h |  2 +-
 2 files changed, 42 insertions(+), 40 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 68454b0de2b1..6caabcd5037e 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -458,8 +458,9 @@ static unsigned long host_idt_base;
  * Though SYSCALL is only supported in 64-bit mode on Intel CPUs, kvm
  * will emulate SYSCALL in legacy mode if the vendor string in guest
  * CPUID.0:{EBX,ECX,EDX} is "AuthenticAMD" or "AMDisbetter!" To
- * support this emulation, IA32_STAR must always be included in
- * vmx_uret_msrs_list[], even in i386 builds.
+ * support this emulation, MSR_STAR is included in the list for i386,
+ * but is never loaded into hardware.  MSR_CSTAR is also never loaded
+ * into hardware and is here purely for emulation purposes.
  */
 static u32 vmx_uret_msrs_list[] = {
 #ifdef CONFIG_X86_64
@@ -702,18 +703,12 @@ static bool is_valid_passthrough_msr(u32 msr)
 	return r;
 }
 
-static inline int __vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr)
+static inline int __vmx_find_uret_msr(u32 msr)
 {
 	int i;
 
-	/*
-	 * Note, vmx->guest_uret_msrs is the same size as vmx_uret_msrs_list,
-	 * but is ordered differently.  The MSR is matched against the list of
-	 * supported uret MSRs using "slot", but the index that is returned is
-	 * the index into guest_uret_msrs.
-	 */
 	for (i = 0; i < vmx_nr_uret_msrs; ++i) {
-		if (vmx_uret_msrs_list[vmx->guest_uret_msrs[i].slot] == msr)
+		if (vmx_uret_msrs_list[i] == msr)
 			return i;
 	}
 	return -1;
@@ -723,7 +718,7 @@ struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr)
 {
 	int i;
 
-	i = __vmx_find_uret_msr(vmx, msr);
+	i = __vmx_find_uret_msr(msr);
 	if (i >= 0)
 		return &vmx->guest_uret_msrs[i];
 	return NULL;
@@ -732,13 +727,14 @@ struct vmx_uret_msr *vmx_find_uret_msr(struct vcpu_vmx *vmx, u32 msr)
 static int vmx_set_guest_uret_msr(struct vcpu_vmx *vmx,
 				  struct vmx_uret_msr *msr, u64 data)
 {
+	unsigned int slot = msr - vmx->guest_uret_msrs;
 	int ret = 0;
 
 	u64 old_msr_data = msr->data;
 	msr->data = data;
-	if (msr - vmx->guest_uret_msrs < vmx->nr_active_uret_msrs) {
+	if (msr->load_into_hardware) {
 		preempt_disable();
-		ret = kvm_set_user_return_msr(msr->slot, msr->data, msr->mask);
+		ret = kvm_set_user_return_msr(slot, msr->data, msr->mask);
 		preempt_enable();
 		if (ret)
 			msr->data = old_msr_data;
@@ -1090,7 +1086,7 @@ static bool update_transition_efer(struct vcpu_vmx *vmx)
 		return false;
 	}
 
-	i = __vmx_find_uret_msr(vmx, MSR_EFER);
+	i = __vmx_find_uret_msr(MSR_EFER);
 	if (i < 0)
 		return false;
 
@@ -1252,11 +1248,14 @@ void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
 	 */
 	if (!vmx->guest_uret_msrs_loaded) {
 		vmx->guest_uret_msrs_loaded = true;
-		for (i = 0; i < vmx->nr_active_uret_msrs; ++i)
-			kvm_set_user_return_msr(vmx->guest_uret_msrs[i].slot,
+		for (i = 0; i < vmx_nr_uret_msrs; ++i) {
+			if (!vmx->guest_uret_msrs[i].load_into_hardware)
+				continue;
+
+			kvm_set_user_return_msr(i,
 						vmx->guest_uret_msrs[i].data,
 						vmx->guest_uret_msrs[i].mask);
-
+		}
 	}
 
     	if (vmx->nested.need_vmcs12_to_shadow_sync)
@@ -1763,19 +1762,16 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu)
 	vmx_clear_hlt(vcpu);
 }
 
-static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr)
+static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr,
+			       bool load_into_hardware)
 {
-	struct vmx_uret_msr tmp;
-	int from, to;
+	struct vmx_uret_msr *uret_msr;
 
-	from = __vmx_find_uret_msr(vmx, msr);
-	if (from < 0)
+	uret_msr = vmx_find_uret_msr(vmx, msr);
+	if (!uret_msr)
 		return;
-	to = vmx->nr_active_uret_msrs++;
 
-	tmp = vmx->guest_uret_msrs[to];
-	vmx->guest_uret_msrs[to] = vmx->guest_uret_msrs[from];
-	vmx->guest_uret_msrs[from] = tmp;
+	uret_msr->load_into_hardware = load_into_hardware;
 }
 
 /*
@@ -1785,30 +1781,36 @@ static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr)
  */
 static void setup_msrs(struct vcpu_vmx *vmx)
 {
-	vmx->guest_uret_msrs_loaded = false;
-	vmx->nr_active_uret_msrs = 0;
 #ifdef CONFIG_X86_64
+	bool load_syscall_msrs;
+
 	/*
 	 * The SYSCALL MSRs are only needed on long mode guests, and only
 	 * when EFER.SCE is set.
 	 */
-	if (is_long_mode(&vmx->vcpu) && (vmx->vcpu.arch.efer & EFER_SCE)) {
-		vmx_setup_uret_msr(vmx, MSR_STAR);
-		vmx_setup_uret_msr(vmx, MSR_LSTAR);
-		vmx_setup_uret_msr(vmx, MSR_SYSCALL_MASK);
-	}
+	load_syscall_msrs = is_long_mode(&vmx->vcpu) &&
+			    (vmx->vcpu.arch.efer & EFER_SCE);
+
+	vmx_setup_uret_msr(vmx, MSR_STAR, load_syscall_msrs);
+	vmx_setup_uret_msr(vmx, MSR_LSTAR, load_syscall_msrs);
+	vmx_setup_uret_msr(vmx, MSR_SYSCALL_MASK, load_syscall_msrs);
 #endif
-	if (update_transition_efer(vmx))
-		vmx_setup_uret_msr(vmx, MSR_EFER);
+	vmx_setup_uret_msr(vmx, MSR_EFER, update_transition_efer(vmx));
 
-	if (guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP)  ||
-	    guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID))
-		vmx_setup_uret_msr(vmx, MSR_TSC_AUX);
+	vmx_setup_uret_msr(vmx, MSR_TSC_AUX,
+			   guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDTSCP) ||
+			   guest_cpuid_has(&vmx->vcpu, X86_FEATURE_RDPID));
 
-	vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL);
+	vmx_setup_uret_msr(vmx, MSR_IA32_TSX_CTRL, true);
 
 	if (cpu_has_vmx_msr_bitmap())
 		vmx_update_msr_bitmap(&vmx->vcpu);
+
+	/*
+	 * The set of MSRs to load may have changed, reload MSRs before the
+	 * next VM-Enter.
+	 */
+	vmx->guest_uret_msrs_loaded = false;
 }
 
 static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index d71ed8b425c5..16e4e457ba23 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -36,7 +36,7 @@ struct vmx_msrs {
 };
 
 struct vmx_uret_msr {
-	unsigned int slot; /* The MSR's slot in kvm_user_return_msrs. */
+	bool load_into_hardware;
 	u64 data;
 	u64 mask;
 };
-- 
2.31.1.527.g47e6f16901-goog


  parent reply	other threads:[~2021-05-04 17:18 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-04 17:17 [PATCH 00/15] KVM: x86: RDPID/RDTSCP fixes and uret MSR cleanups Sean Christopherson
2021-05-04 17:17 ` [PATCH 01/15] KVM: VMX: Do not adverise RDPID if ENABLE_RDTSCP control is unsupported Sean Christopherson
2021-05-04 17:37   ` Jim Mattson
2021-05-04 17:53     ` Jim Mattson
2021-05-04 18:14       ` Sean Christopherson
2021-05-05  3:04   ` Reiji Watanabe
2021-05-10  8:03   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 02/15] KVM: x86: Emulate RDPID only if RDTSCP is supported Sean Christopherson
2021-05-04 17:50   ` Jim Mattson
2021-05-05  3:51   ` Reiji Watanabe
2021-05-05  8:01     ` Paolo Bonzini
2021-05-10  8:08   ` Maxim Levitsky
2021-05-10 17:20     ` Sean Christopherson
2021-05-11 12:32       ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest Sean Christopherson
2021-05-04 21:45   ` Jim Mattson
2021-05-04 21:53     ` Sean Christopherson
2021-05-04 21:56       ` Jim Mattson
2021-05-04 22:10         ` Sean Christopherson
2021-05-04 22:24           ` Jim Mattson
2021-05-04 21:57       ` Paolo Bonzini
2021-05-04 21:58         ` Jim Mattson
2021-05-10  8:08           ` Maxim Levitsky
2021-05-10 16:56             ` Sean Christopherson
2021-05-11 12:34               ` Maxim Levitsky
2021-05-18 10:59               ` Paolo Bonzini
2021-05-18 19:24                 ` Sean Christopherson
2021-05-05  4:26   ` Reiji Watanabe
2021-05-10  8:08   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 04/15] KVM: x86: Move RDPID emulation intercept to its own enum Sean Christopherson
2021-05-04 23:24   ` Jim Mattson
2021-05-10  8:14   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 05/15] KVM: VMX: Disable preemption when probing user return MSRs Sean Christopherson
2021-05-04 23:36   ` Jim Mattson
2021-05-10  8:18   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 06/15] KVM: SVM: Probe and load MSR_TSC_AUX regardless of RDTSCP support in host Sean Christopherson
2021-05-10  8:20   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 07/15] KVM: x86: Add support for RDPID without RDTSCP Sean Christopherson
2021-05-10  8:20   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 08/15] KVM: VMX: Configure list of user return MSRs at module init Sean Christopherson
2021-05-10  8:23   ` Maxim Levitsky
2021-05-10 15:13     ` Sean Christopherson
2021-05-11 12:34       ` Maxim Levitsky
2021-05-11 20:10         ` Sean Christopherson
2021-05-04 17:17 ` Sean Christopherson [this message]
2021-05-08  3:31   ` [PATCH 09/15] KVM: VMX: Use flag to indicate "active" uret MSRs instead of sorting list Reiji Watanabe
2021-05-10 16:43     ` Sean Christopherson
2021-05-10 17:55       ` Reiji Watanabe
2021-05-10  8:25   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 10/15] KVM: VMX: Use common x86's uret MSR list as the one true list Sean Christopherson
2021-05-10  8:25   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 11/15] KVM: VMX: Disable loading of TSX_CTRL MSR the more conventional way Sean Christopherson
2021-05-05  8:49   ` Paolo Bonzini
2021-05-05 15:36     ` Sean Christopherson
2021-05-05 15:50       ` Paolo Bonzini
2021-05-10  8:26   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 12/15] KVM: x86: Export the number of uret MSRs to vendor modules Sean Christopherson
2021-05-10  8:27   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 13/15] KVM: x86: Move uret MSR slot management to common x86 Sean Christopherson
2021-05-10  8:28   ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 14/15] KVM: x86: Tie Intel and AMD behavior for MSR_TSC_AUX to guest CPU model Sean Christopherson
2021-05-10  8:29   ` Maxim Levitsky
2021-05-10 16:50     ` Sean Christopherson
2021-05-10 17:11       ` Jim Mattson
2021-05-11 12:34         ` Maxim Levitsky
2021-05-04 17:17 ` [PATCH 15/15] KVM: x86: Hide RDTSCP and RDPID if MSR_TSC_AUX probing failed Sean Christopherson
2021-05-10  8:29   ` Maxim Levitsky
2021-05-05  8:51 ` [PATCH 00/15] KVM: x86: RDPID/RDTSCP fixes and uret MSR cleanups Paolo Bonzini

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