The patch below does not apply to the 5.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 0caa0a77c2f6fcd0830cdcd018db1af98fe35e28 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@xxxxxxxxxx>
Date: Tue, 4 May 2021 10:17:25 -0700
Subject: [PATCH] KVM: SVM: Probe and load MSR_TSC_AUX regardless of RDTSCP
support in host
Probe MSR_TSC_AUX whether or not RDTSCP is supported in the host, and
if probing succeeds, load the guest's MSR_TSC_AUX into hardware prior to
VMRUN. Because SVM doesn't support interception of RDPID, RDPID cannot
be disallowed in the guest (without resorting to binary translation).
Leaving the host's MSR_TSC_AUX in hardware would leak the host's value to
the guest if RDTSCP is not supported.
Note, there is also a kernel bug that prevents leaking the host's value.
The host kernel initializes MSR_TSC_AUX if and only if RDTSCP is
supported, even though the vDSO usage consumes MSR_TSC_AUX via RDPID.
I.e. if RDTSCP is not supported, there is no host value to leak. But,
if/when the host kernel bug is fixed, KVM would start leaking MSR_TSC_AUX
in the case where hardware supports RDPID but RDTSCP is unavailable for
whatever reason.
Probing MSR_TSC_AUX will also allow consolidating the probe and define
logic in common x86, and will make it simpler to condition the existence
of MSR_TSX_AUX (from the guest's perspective) on RDTSCP *or* RDPID.
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20210504171734.1434054-7-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ebcb5849d69b..13e4dd128177 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -212,7 +212,7 @@ DEFINE_PER_CPU(struct svm_cpu_data *, svm_data);
* RDTSCP and RDPID are not used in the kernel, specifically to allow KVM to
* defer the restoration of TSC_AUX until the CPU returns to userspace.
*/
-#define TSC_AUX_URET_SLOT 0
+static int tsc_aux_uret_slot __read_mostly = -1;
static const u32 msrpm_ranges[] = {0, 0xc0000000, 0xc0010000};
@@ -959,8 +959,10 @@ static __init int svm_hardware_setup(void)
kvm_tsc_scaling_ratio_frac_bits = 32;
}
- if (boot_cpu_has(X86_FEATURE_RDTSCP))
- kvm_define_user_return_msr(TSC_AUX_URET_SLOT, MSR_TSC_AUX);
+ if (!kvm_probe_user_return_msr(MSR_TSC_AUX)) {
+ tsc_aux_uret_slot = 0;
+ kvm_define_user_return_msr(tsc_aux_uret_slot, MSR_TSC_AUX);
+ }
/* Check for pause filtering support */
if (!boot_cpu_has(X86_FEATURE_PAUSEFILTER)) {
@@ -1454,8 +1456,8 @@ static void svm_prepare_guest_switch(struct kvm_vcpu *vcpu)
}
}
- if (static_cpu_has(X86_FEATURE_RDTSCP))
- kvm_set_user_return_msr(TSC_AUX_URET_SLOT, svm->tsc_aux, -1ull);
+ if (likely(tsc_aux_uret_slot >= 0))
+ kvm_set_user_return_msr(tsc_aux_uret_slot, svm->tsc_aux, -1ull);
svm->guest_state_loaded = true;
}
@@ -2664,7 +2666,7 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data |= (u64)svm->sysenter_esp_hi << 32;
break;
case MSR_TSC_AUX:
- if (!boot_cpu_has(X86_FEATURE_RDTSCP))
+ if (tsc_aux_uret_slot < 0)
return 1;
if (!msr_info->host_initiated &&
!guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
@@ -2885,7 +2887,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
svm->sysenter_esp_hi = guest_cpuid_is_intel(vcpu) ? (data >> 32) : 0;
break;
case MSR_TSC_AUX:
- if (!boot_cpu_has(X86_FEATURE_RDTSCP))
+ if (tsc_aux_uret_slot < 0)
return 1;
if (!msr->host_initiated &&
@@ -2908,7 +2910,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
* guest via direct_access_msrs, and switch it via user return.
*/
preempt_disable();
- r = kvm_set_user_return_msr(TSC_AUX_URET_SLOT, data, -1ull);
+ r = kvm_set_user_return_msr(tsc_aux_uret_slot, data, -1ull);
preempt_enable();
if (r)
return 1;
