linux-kernel - [PATCH v4 14/19] KVM: SVM: Check that the current CPU supports SVM in kvm_is_svm

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Message-ID: <20230721201859.2307736-15-seanjc@google.com>
Date:   Fri, 21 Jul 2023 13:18:54 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Kai Huang <kai.huang@...el.com>, Chao Gao <chao.gao@...el.com>
Subject: [PATCH v4 14/19] KVM: SVM: Check that the current CPU supports SVM in kvm_is_svm_supported()

Check "this" CPU instead of the boot CPU when querying SVM support so that
the per-CPU checks done during hardware enabling actually function as
intended, i.e. will detect issues where SVM isn't support on all CPUs.

Disable migration for the use from svm_init() mostly so that the standard
accessors for the per-CPU data can be used without getting yelled at by
CONFIG_DEBUG_PREEMPT=y sanity checks.  Preventing the "disabled by BIOS"
error message from reporting the wrong CPU is largely a bonus, as ensuring
a stable CPU during module load is a non-goal for KVM.

Link: https://lore.kernel.org/all/ZAdxNgv0M6P63odE@google.com
Cc: Kai Huang <kai.huang@...el.com>
Cc: Chao Gao <chao.gao@...el.com>
Reviewed-by: Kai Huang <kai.huang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ff6c769aafb2..9e449167e71b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -518,18 +518,20 @@ static void svm_init_osvw(struct kvm_vcpu *vcpu)
 		vcpu->arch.osvw.status |= 1;
 }
 
-static bool kvm_is_svm_supported(void)
+static bool __kvm_is_svm_supported(void)
 {
-	int cpu = raw_smp_processor_id();
+	int cpu = smp_processor_id();
+	struct cpuinfo_x86 *c = &cpu_data(cpu);
+
 	u64 vm_cr;
 
-	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
-	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON) {
+	if (c->x86_vendor != X86_VENDOR_AMD &&
+	    c->x86_vendor != X86_VENDOR_HYGON) {
 		pr_err("CPU %d isn't AMD or Hygon\n", cpu);
 		return false;
 	}
 
-	if (!boot_cpu_has(X86_FEATURE_SVM)) {
+	if (!cpu_has(c, X86_FEATURE_SVM)) {
 		pr_err("SVM not supported by CPU %d\n", cpu);
 		return false;
 	}
@@ -548,9 +550,20 @@ static bool kvm_is_svm_supported(void)
 	return true;
 }
 
+static bool kvm_is_svm_supported(void)
+{
+	bool supported;
+
+	migrate_disable();
+	supported = __kvm_is_svm_supported();
+	migrate_enable();
+
+	return supported;
+}
+
 static int svm_check_processor_compat(void)
 {
-	if (!kvm_is_svm_supported())
+	if (!__kvm_is_svm_supported())
 		return -EIO;
 
 	return 0;
-- 
2.41.0.487.g6d72f3e995-goog