linux-kernel - [PATCH v2 09/32] KVM: SVM: Clean up macros related to architectural MSRPM definitions

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Message-ID: <20250610225737.156318-10-seanjc@google.com>
Date: Tue, 10 Jun 2025 15:57:14 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chao Gao <chao.gao@...el.com>, Borislav Petkov <bp@...en8.de>, Xin Li <xin@...or.com>, 
	Dapeng Mi <dapeng1.mi@...ux.intel.com>, Francesco Lavra <francescolavra.fl@...il.com>, 
	Manali Shukla <Manali.Shukla@....com>
Subject: [PATCH v2 09/32] KVM: SVM: Clean up macros related to architectural
 MSRPM definitions

Move SVM's MSR Permissions Map macros to svm.h in antipication of adding
helpers that are available to SVM code, and opportunistically replace a
variety of open-coded literals with (hopefully) informative macros.

Opportunistically open code ARRAY_SIZE(msrpm_ranges) instead of wrapping
it as NUM_MSR_MAPS, which is an ambiguous name even if it were qualified
with "SVM_MSRPM".

Deliberately leave the ranges as open coded literals, as using macros to
define the ranges actually introduces more potential failure points, since
both the definitions and the usage have to be careful to use the correct
index.  The lack of clear intent behind the ranges will be addressed in
future patches.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 12 ++++--------
 arch/x86/kvm/svm/svm.h | 13 ++++++++++++-
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 854904a80b7e..a683602cae22 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -268,22 +268,18 @@ static int tsc_aux_uret_slot __read_mostly = -1;
 
 static const u32 msrpm_ranges[] = {0, 0xc0000000, 0xc0010000};
 
-#define NUM_MSR_MAPS ARRAY_SIZE(msrpm_ranges)
-#define MSRS_RANGE_SIZE 2048
-#define MSRS_IN_RANGE (MSRS_RANGE_SIZE * 8 / 2)
-
 u32 svm_msrpm_offset(u32 msr)
 {
 	u32 offset;
 	int i;
 
-	for (i = 0; i < NUM_MSR_MAPS; i++) {
+	for (i = 0; i < ARRAY_SIZE(msrpm_ranges); i++) {
 		if (msr < msrpm_ranges[i] ||
-		    msr >= msrpm_ranges[i] + MSRS_IN_RANGE)
+		    msr >= msrpm_ranges[i] + SVM_MSRS_PER_RANGE)
 			continue;
 
-		offset  = (msr - msrpm_ranges[i]) / 4; /* 4 msrs per u8 */
-		offset += (i * MSRS_RANGE_SIZE);       /* add range offset */
+		offset  = (msr - msrpm_ranges[i]) / SVM_MSRS_PER_BYTE;
+		offset += (i * SVM_MSRPM_BYTES_PER_RANGE);  /* add range offset */
 
 		/* Now we have the u8 offset - but need the u32 offset */
 		return offset / 4;
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index f1e466a10219..086a8c8aae86 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -613,11 +613,22 @@ static inline void svm_vmgexit_no_action(struct vcpu_svm *svm, u64 data)
 	svm_vmgexit_set_return_code(svm, GHCB_HV_RESP_NO_ACTION, data);
 }
 
-/* svm.c */
+/*
+ * The MSRPM is 8KiB in size, divided into four 2KiB ranges (the fourth range
+ * is reserved).  Each MSR within a range is covered by two bits, one each for
+ * read (bit 0) and write (bit 1), where a bit value of '1' means intercepted.
+ */
+#define SVM_MSRPM_BYTES_PER_RANGE 2048
+#define SVM_BITS_PER_MSR 2
+#define SVM_MSRS_PER_BYTE (BITS_PER_BYTE / SVM_BITS_PER_MSR)
+#define SVM_MSRS_PER_RANGE (SVM_MSRPM_BYTES_PER_RANGE * SVM_MSRS_PER_BYTE)
+static_assert(SVM_MSRS_PER_RANGE == 8192);
+
 #define MSR_INVALID				0xffffffffU
 
 #define DEBUGCTL_RESERVED_BITS (~DEBUGCTLMSR_LBR)
 
+/* svm.c */
 extern bool dump_invalid_vmcb;
 
 u32 svm_msrpm_offset(u32 msr);
-- 
2.50.0.rc0.642.g800a2b2222-goog