From: Sean Christopherson <seanjc@google.com>
Date: Tue, 10 Jun 2025 22:57:10 +0000 (-0700)
Subject: KVM: SVM: Use ARRAY_SIZE() to iterate over direct_access_msrs
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b241c50c4e30877a7b9dcf2517762748d86e5d47;p=thirdparty%2Flinux.git

KVM: SVM: Use ARRAY_SIZE() to iterate over direct_access_msrs

Drop the unnecessary and dangerous value-terminated behavior of
direct_access_msrs, and simply iterate over the actual size of the array.
The use in svm_set_x2apic_msr_interception() is especially sketchy, as it
relies on unused capacity being zero-initialized, and '0' being outside
the range of x2APIC MSRs.

To ensure the array and shadow_msr_intercept stay synchronized, simply
assert that their sizes are identical (note the six 64-bit-only MSRs).

Note, direct_access_msrs will soon be removed entirely; keeping the assert
synchronized with the array isn't expected to be along-term maintenance
burden.

Reviewed-by: Chao Gao <chao.gao@intel.com>
Link: https://lore.kernel.org/r/20250610225737.156318-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
---

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 127b54c1bbaf5..703aa000c8691 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -87,7 +87,7 @@ static DEFINE_PER_CPU(u64, current_tsc_ratio);
 static const struct svm_direct_access_msrs {
 	u32 index;   /* Index of the MSR */
 	bool always; /* True if intercept is initially cleared */
-} direct_access_msrs[MAX_DIRECT_ACCESS_MSRS] = {
+} direct_access_msrs[] = {
 	{ .index = MSR_STAR,				.always = true  },
 	{ .index = MSR_IA32_SYSENTER_CS,		.always = true  },
 	{ .index = MSR_IA32_SYSENTER_EIP,		.always = false },
@@ -145,9 +145,12 @@ static const struct svm_direct_access_msrs {
 	{ .index = X2APIC_MSR(APIC_TMICT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TMCCT),		.always = false },
 	{ .index = X2APIC_MSR(APIC_TDCR),		.always = false },
-	{ .index = MSR_INVALID,				.always = false },
 };
 
+static_assert(ARRAY_SIZE(direct_access_msrs) ==
+	      MAX_DIRECT_ACCESS_MSRS - 6 * !IS_ENABLED(CONFIG_X86_64));
+#undef MAX_DIRECT_ACCESS_MSRS
+
 /*
  * These 2 parameters are used to config the controls for Pause-Loop Exiting:
  * pause_filter_count: On processors that support Pause filtering(indicated
@@ -761,9 +764,10 @@ static int direct_access_msr_slot(u32 msr)
 {
 	u32 i;
 
-	for (i = 0; direct_access_msrs[i].index != MSR_INVALID; i++)
+	for (i = 0; i < ARRAY_SIZE(direct_access_msrs); i++) {
 		if (direct_access_msrs[i].index == msr)
 			return i;
+	}
 
 	return -ENOENT;
 }
@@ -885,7 +889,7 @@ void svm_vcpu_init_msrpm(struct kvm_vcpu *vcpu, u32 *msrpm)
 {
 	int i;
 
-	for (i = 0; direct_access_msrs[i].index != MSR_INVALID; i++) {
+	for (i = 0; i < ARRAY_SIZE(direct_access_msrs); i++) {
 		if (!direct_access_msrs[i].always)
 			continue;
 		set_msr_interception(vcpu, msrpm, direct_access_msrs[i].index, 1, 1);
@@ -902,7 +906,7 @@ void svm_set_x2apic_msr_interception(struct vcpu_svm *svm, bool intercept)
 	if (!x2avic_enabled)
 		return;
 
-	for (i = 0; i < MAX_DIRECT_ACCESS_MSRS; i++) {
+	for (i = 0; i < ARRAY_SIZE(direct_access_msrs); i++) {
 		int index = direct_access_msrs[i].index;
 
 		if ((index < APIC_BASE_MSR) ||
@@ -930,7 +934,7 @@ static void svm_msr_filter_changed(struct kvm_vcpu *vcpu)
 	 * will automatically get filtered through the MSR filter, so we are
 	 * back in sync after this.
 	 */
-	for (i = 0; direct_access_msrs[i].index != MSR_INVALID; i++) {
+	for (i = 0; i < ARRAY_SIZE(direct_access_msrs); i++) {
 		u32 msr = direct_access_msrs[i].index;
 		u32 read = test_bit(i, svm->shadow_msr_intercept.read);
 		u32 write = test_bit(i, svm->shadow_msr_intercept.write);
@@ -968,7 +972,7 @@ static __init int init_msrpm_offsets(void)
 
 	memset(msrpm_offsets, 0xff, sizeof(msrpm_offsets));
 
-	for (i = 0; direct_access_msrs[i].index != MSR_INVALID; i++) {
+	for (i = 0; i < ARRAY_SIZE(direct_access_msrs); i++) {
 		u32 offset;
 
 		offset = svm_msrpm_offset(direct_access_msrs[i].index);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e6f3c6a153a0c..f1e466a10219b 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -44,7 +44,7 @@ static inline struct page *__sme_pa_to_page(unsigned long pa)
 #define	IOPM_SIZE PAGE_SIZE * 3
 #define	MSRPM_SIZE PAGE_SIZE * 2
 
-#define MAX_DIRECT_ACCESS_MSRS	48
+#define MAX_DIRECT_ACCESS_MSRS	47
 #define MSRPM_OFFSETS	32
 extern u32 msrpm_offsets[MSRPM_OFFSETS] __read_mostly;
 extern bool npt_enabled;