x86/sev: Guard sev_evict_cache() with CONFIG_AMD_MEM_ENCRYPT

The sev_evict_cache() is guest-related code and should be guarded by
CONFIG_AMD_MEM_ENCRYPT, not CONFIG_KVM_AMD_SEV.

CONFIG_AMD_MEM_ENCRYPT=y is required for a guest to run properly as an SEV-SNP
guest, but a guest kernel built with CONFIG_KVM_AMD_SEV=n would get the stub
function of sev_evict_cache() instead of the version that performs the actual
eviction. Move the function declarations under the appropriate #ifdef.

Fixes: 7b306df ("x86/sev: Evict cache lines during SNP memory validation")
Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Cc: [email protected] # 6.16.x
Link: https://lore.kernel.org/r/70e38f2c4a549063de54052c9f64929705313526.1757708959.git.thomas.lendacky@amd.com

Author: tlendacky

arch/x86/include/asm/sev.h

@@ -562,6 +562,24 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
 
 extern struct ghcb *boot_ghcb;
 
+static inline void sev_evict_cache(void *va, int npages)
+{
+	volatile u8 val __always_unused;
+	u8 *bytes = va;
+	int page_idx;
+
+	/*
+	 * For SEV guests, a read from the first/last cache-lines of a 4K page
+	 * using the guest key is sufficient to cause a flush of all cache-lines
+	 * associated with that 4K page without incurring all the overhead of a
+	 * full CLFLUSH sequence.
+	 */
+	for (page_idx = 0; page_idx < npages; page_idx++) {
+		val = bytes[page_idx * PAGE_SIZE];
+		val = bytes[page_idx * PAGE_SIZE + PAGE_SIZE - 1];
+	}
+}
+
 #else	/* !CONFIG_AMD_MEM_ENCRYPT */
 
 #define snp_vmpl 0
@@ -605,6 +623,7 @@ static inline int snp_send_guest_request(struct snp_msg_desc *mdesc,
 static inline int snp_svsm_vtpm_send_command(u8 *buffer) { return -ENODEV; }
 static inline void __init snp_secure_tsc_prepare(void) { }
 static inline void __init snp_secure_tsc_init(void) { }
+static inline void sev_evict_cache(void *va, int npages) {}
 
 #endif	/* CONFIG_AMD_MEM_ENCRYPT */
 
@@ -619,24 +638,6 @@ int rmp_make_shared(u64 pfn, enum pg_level level);
 void snp_leak_pages(u64 pfn, unsigned int npages);
 void kdump_sev_callback(void);
 void snp_fixup_e820_tables(void);
-
-static inline void sev_evict_cache(void *va, int npages)
-{
-	volatile u8 val __always_unused;
-	u8 *bytes = va;
-	int page_idx;
-
-	/*
-	 * For SEV guests, a read from the first/last cache-lines of a 4K page
-	 * using the guest key is sufficient to cause a flush of all cache-lines
-	 * associated with that 4K page without incurring all the overhead of a
-	 * full CLFLUSH sequence.
-	 */
-	for (page_idx = 0; page_idx < npages; page_idx++) {
-		val = bytes[page_idx * PAGE_SIZE];
-		val = bytes[page_idx * PAGE_SIZE + PAGE_SIZE - 1];
-	}
-}
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }
 static inline int snp_rmptable_init(void) { return -ENOSYS; }
@@ -652,7 +653,6 @@ static inline int rmp_make_shared(u64 pfn, enum pg_level level) { return -ENODEV
 static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
-static inline void sev_evict_cache(void *va, int npages) {}
 #endif
 
 #endif