linux-kernel - [kvm-unit-tests 3/7] x86/svm: Add FEP helpers for SVM tests

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Message-ID: <20251024194925.3201933-4-yosry.ahmed@linux.dev>
Date: Fri, 24 Oct 2025 19:49:21 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	Jim Mattson <jmattson@...gle.com>,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yosry Ahmed <yosryahmed@...gle.com>
Subject: [kvm-unit-tests 3/7] x86/svm: Add FEP helpers for SVM tests

From: Yosry Ahmed <yosryahmed@...gle.com>

Add helpers to check if FEP is enabled to use as supported() callbacks
in SVM tests for the emulator. Also add a macro that executes an
assembly instruction conditionally with FEP, which will make writing
SVM tests that run with and without FEP more convenient.

Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>
---
 lib/x86/desc.h | 8 ++++++++
 x86/svm.c      | 5 +++++
 x86/svm.h      | 1 +
 3 files changed, 14 insertions(+)

diff --git a/lib/x86/desc.h b/lib/x86/desc.h
index 68f38f3d..06c8be65 100644
--- a/lib/x86/desc.h
+++ b/lib/x86/desc.h
@@ -284,6 +284,14 @@ extern unsigned long get_gdt_entry_limit(gdt_entry_t *entry);
 #define asm_fep_safe(insn, inputs...)				\
 	__asm_safe_out1(KVM_FEP, insn,, inputs)
 
+#define asm_conditional_fep_safe(fep, insn, inputs...)			\
+({									\
+	if (fep)							\
+		asm_fep_safe(insn, inputs);				\
+	else								\
+		asm_safe(insn, inputs);					\
+})
+
 #define __asm_safe_out1(fep, insn, output, inputs...)			\
 ({									\
 	asm volatile(__ASM_TRY(fep, "1f")				\
diff --git a/x86/svm.c b/x86/svm.c
index e715e270..035367a1 100644
--- a/x86/svm.c
+++ b/x86/svm.c
@@ -53,6 +53,11 @@ bool default_supported(void)
 	return true;
 }
 
+bool fep_supported(void)
+{
+	return is_fep_available;
+}
+
 bool vgif_supported(void)
 {
 	return this_cpu_has(X86_FEATURE_VGIF);
diff --git a/x86/svm.h b/x86/svm.h
index c1dd84af..264583a6 100644
--- a/x86/svm.h
+++ b/x86/svm.h
@@ -417,6 +417,7 @@ u64 *npt_get_pdpe(u64 address);
 u64 *npt_get_pml4e(void);
 bool smp_supported(void);
 bool default_supported(void);
+bool fep_supported(void);
 bool vgif_supported(void);
 bool lbrv_supported(void);
 bool tsc_scale_supported(void);
-- 
2.51.1.821.gb6fe4d2222-goog