From: KarimAllah Ahmed <karahmed@amazon.de>
To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org
Cc: KarimAllah Ahmed <karahmed@amazon.de>,
Asit Mallick <asit.k.mallick@intel.com>,
Arjan Van De Ven <arjan.van.de.ven@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Andi Kleen <ak@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Dan Williams <dan.j.williams@intel.com>,
Jun Nakajima <jun.nakajima@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
David Woodhouse <dwmw@amazon.co.uk>,
Greg KH <gregkh@linuxfoundation.org>,
Andy Lutomirski <luto@kernel.org>,
Ashok Raj <ashok.raj@intel.com>
Subject: [PATCH v6 5/5] KVM: SVM: Allow direct access to MSR_IA32_SPEC_CTRL
Date: Thu, 1 Feb 2018 22:59:46 +0100 [thread overview]
Message-ID: <1517522386-18410-6-git-send-email-karahmed@amazon.de> (raw)
In-Reply-To: <1517522386-18410-1-git-send-email-karahmed@amazon.de>
[ Based on a patch from Paolo Bonzini <pbonzini@redhat.com> ]
... basically doing exactly what we do for VMX:
- Passthrough SPEC_CTRL to guests (if enabled in guest CPUID)
- Save and restore SPEC_CTRL around VMExit and VMEntry only if the guest
actually used it.
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan Van De Ven <arjan.van.de.ven@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jun Nakajima <jun.nakajima@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
v5:
- Add SPEC_CTRL to direct_access_msrs.
---
arch/x86/kvm/svm.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 59 insertions(+)
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 254eefb..c6ab343 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -184,6 +184,9 @@ struct vcpu_svm {
u64 gs_base;
} host;
+ u64 spec_ctrl;
+ bool save_spec_ctrl_on_exit;
+
u32 *msrpm;
ulong nmi_iret_rip;
@@ -249,6 +252,7 @@ static const struct svm_direct_access_msrs {
{ .index = MSR_CSTAR, .always = true },
{ .index = MSR_SYSCALL_MASK, .always = true },
#endif
+ { .index = MSR_IA32_SPEC_CTRL, .always = false },
{ .index = MSR_IA32_PRED_CMD, .always = false },
{ .index = MSR_IA32_LASTBRANCHFROMIP, .always = false },
{ .index = MSR_IA32_LASTBRANCHTOIP, .always = false },
@@ -1584,6 +1588,8 @@ static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
u32 dummy;
u32 eax = 1;
+ svm->spec_ctrl = 0;
+
if (!init_event) {
svm->vcpu.arch.apic_base = APIC_DEFAULT_PHYS_BASE |
MSR_IA32_APICBASE_ENABLE;
@@ -3605,6 +3611,13 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
case MSR_VM_CR:
msr_info->data = svm->nested.vm_cr_msr;
break;
+ case MSR_IA32_SPEC_CTRL:
+ if (!msr_info->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_IBRS))
+ return 1;
+
+ msr_info->data = svm->spec_ctrl;
+ break;
case MSR_IA32_UCODE_REV:
msr_info->data = 0x01000065;
break;
@@ -3696,6 +3709,30 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
case MSR_IA32_TSC:
kvm_write_tsc(vcpu, msr);
break;
+ case MSR_IA32_SPEC_CTRL:
+ if (!msr->host_initiated &&
+ !guest_cpuid_has(vcpu, X86_FEATURE_IBRS))
+ return 1;
+
+ /* The STIBP bit doesn't fault even if it's not advertised */
+ if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP))
+ return 1;
+
+ svm->spec_ctrl = data;
+
+ /*
+ * When it's written (to non-zero) for the first time, pass
+ * it through. This means we don't have to take the perf
+ * hit of saving it on vmexit for the common case of guests
+ * that don't use it.
+ */
+ if (data && !svm->save_spec_ctrl_on_exit) {
+ svm->save_spec_ctrl_on_exit = true;
+ if (is_guest_mode(vcpu))
+ break;
+ set_msr_interception(svm->msrpm, MSR_IA32_SPEC_CTRL, 1, 1);
+ }
+ break;
case MSR_IA32_PRED_CMD:
if (!msr->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_IBPB))
@@ -4964,6 +5001,15 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
local_irq_enable();
+ /*
+ * If this vCPU has touched SPEC_CTRL, restore the guest's value if
+ * it's non-zero. Since vmentry is serialising on affected CPUs, there
+ * is no need to worry about the conditional branch over the wrmsr
+ * being speculatively taken.
+ */
+ if (svm->spec_ctrl)
+ wrmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+
asm volatile (
"push %%" _ASM_BP "; \n\t"
"mov %c[rbx](%[svm]), %%" _ASM_BX " \n\t"
@@ -5056,6 +5102,19 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
#endif
);
+ /*
+ * We do not use IBRS in the kernel. If this vCPU has used the
+ * SPEC_CTRL MSR it may have left it on; save the value and
+ * turn it off. This is much more efficient than blindly adding
+ * it to the atomic save/restore list. Especially as the former
+ * (Saving guest MSRs on vmexit) doesn't even exist in KVM.
+ */
+ if (svm->save_spec_ctrl_on_exit)
+ rdmsrl(MSR_IA32_SPEC_CTRL, svm->spec_ctrl);
+
+ if (svm->spec_ctrl)
+ wrmsrl(MSR_IA32_SPEC_CTRL, 0);
+
/* Eliminate branch target predictions from guest mode */
vmexit_fill_RSB();
--
2.7.4
next prev parent reply other threads:[~2018-02-01 21:59 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-01 21:59 [PATCH v6 0/5] KVM: Expose speculation control feature to guests KarimAllah Ahmed
2018-02-01 21:59 ` [PATCH v6 1/5] KVM: x86: Update the reverse_cpuid list to include CPUID_7_EDX KarimAllah Ahmed
2018-02-02 17:37 ` Jim Mattson
2018-02-03 22:50 ` [tip:x86/pti] KVM/x86: " tip-bot for KarimAllah Ahmed
2018-02-01 21:59 ` [PATCH v6 2/5] KVM: x86: Add IBPB support KarimAllah Ahmed
2018-02-02 17:49 ` Konrad Rzeszutek Wilk
2018-02-02 18:02 ` David Woodhouse
2018-02-02 19:56 ` Konrad Rzeszutek Wilk
2018-02-02 20:16 ` David Woodhouse
2018-02-02 20:28 ` Konrad Rzeszutek Wilk
2018-02-02 20:31 ` David Woodhouse
2018-02-02 20:52 ` Konrad Rzeszutek Wilk
2018-02-02 20:52 ` Alan Cox
2018-02-05 19:22 ` Paolo Bonzini
2018-02-05 19:24 ` Paolo Bonzini
2018-02-03 22:50 ` [tip:x86/pti] KVM/x86: " tip-bot for Ashok Raj
2018-02-16 3:44 ` [PATCH v6 2/5] KVM: x86: " Jim Mattson
2018-02-16 4:22 ` Andi Kleen
2018-05-03 1:27 ` Wanpeng Li
2018-05-03 9:19 ` Paolo Bonzini
2018-05-03 12:01 ` Wanpeng Li
2018-05-03 12:46 ` Tian, Kevin
2018-02-01 21:59 ` [PATCH v6 3/5] KVM: VMX: Emulate MSR_IA32_ARCH_CAPABILITIES KarimAllah Ahmed
2018-02-02 10:53 ` Darren Kenny
2018-02-02 17:35 ` Jim Mattson
2018-02-02 17:51 ` Konrad Rzeszutek Wilk
2018-02-03 22:51 ` [tip:x86/pti] KVM/VMX: " tip-bot for KarimAllah Ahmed
2018-02-01 21:59 ` [PATCH v6 4/5] KVM: VMX: Allow direct access to MSR_IA32_SPEC_CTRL KarimAllah Ahmed
2018-02-02 11:03 ` Darren Kenny
2018-02-02 11:27 ` David Woodhouse
2018-02-02 17:53 ` Konrad Rzeszutek Wilk
2018-02-02 18:05 ` David Woodhouse
2018-02-02 18:19 ` Konrad Rzeszutek Wilk
2018-02-02 17:57 ` Jim Mattson
2018-02-03 22:51 ` [tip:x86/pti] KVM/VMX: " tip-bot for KarimAllah Ahmed
2018-02-01 21:59 ` KarimAllah Ahmed [this message]
2018-02-02 11:06 ` [PATCH v6 5/5] KVM: SVM: " Darren Kenny
2018-02-02 18:02 ` Konrad Rzeszutek Wilk
-- strict thread matches above, loose matches on Subject: below --
2018-01-12 1:32 [PATCH 0/5] Add support for IBRS & IBPB KVM support Ashok Raj
2018-01-12 1:32 ` [PATCH 1/5] x86/ibrs: Introduce native_rdmsrl, and native_wrmsrl Ashok Raj
2018-01-12 1:41 ` Andy Lutomirski
2018-01-12 1:52 ` Raj, Ashok
2018-01-12 2:20 ` Andy Lutomirski
2018-01-12 3:01 ` Raj, Ashok
2018-01-12 5:03 ` Dave Hansen
2018-01-12 16:28 ` Josh Poimboeuf
2018-01-12 16:28 ` Woodhouse, David
2018-01-13 6:20 ` Andy Lutomirski
2018-01-13 13:52 ` Van De Ven, Arjan
2018-01-13 15:20 ` Andy Lutomirski
2018-01-13 6:19 ` Andy Lutomirski
2018-01-12 7:54 ` Greg KH
2018-01-12 12:28 ` Borislav Petkov
2018-01-12 1:32 ` [PATCH 2/5] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC_CTRL Ashok Raj
2018-01-12 1:32 ` [PATCH 3/5] x86/ibrs: Add direct access support for MSR_IA32_SPEC_CTRL Ashok Raj
2018-01-12 1:58 ` Dave Hansen
2018-01-12 3:14 ` Raj, Ashok
2018-01-12 9:51 ` Peter Zijlstra
2018-01-12 10:09 ` David Woodhouse
2018-01-15 13:45 ` Peter Zijlstra
2018-01-15 13:59 ` David Woodhouse
2018-01-15 14:45 ` Peter Zijlstra
2018-01-12 1:32 ` [PATCH 4/5] x86/svm: Direct access to MSR_IA32_SPEC_CTRL Ashok Raj
2018-01-12 7:23 ` David Woodhouse
2018-01-12 9:58 ` Peter Zijlstra
2018-01-12 10:13 ` David Woodhouse
2018-01-12 12:38 ` Paolo Bonzini
2018-01-12 15:14 ` Tom Lendacky
2018-01-12 1:32 ` [PATCH 5/5] x86/feature: Detect the x86 feature Indirect Branch Prediction Barrier Ashok Raj
2018-01-12 10:08 ` Peter Zijlstra
2018-01-12 12:32 ` Borislav Petkov
2018-01-12 12:39 ` Woodhouse, David
2018-01-12 15:21 ` Tom Lendacky
2018-01-12 15:31 ` Tom Lendacky
2018-01-12 15:36 ` Woodhouse, David
2018-01-12 17:06 ` Tom Lendacky
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