x86/sev: Save the negotiated GHCB version

The SEV-ES guest calls sev_es_negotiate_protocol() to negotiate the GHCB
protocol version before establishing the GHCB. Cache the negotiated GHCB
version so that it can be used later.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Venu Busireddy <venu.busireddy@oracle.com>
Link: https://lore.kernel.org/r/20220307213356.2797205-12-brijesh.singh@amd.com

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ec060c4..9b9c190 100644 (file)
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -12,7 +12,7 @@
 #include <asm/insn.h>
 #include <asm/sev-common.h>
 
-#define GHCB_PROTO_OUR         0x0001UL
+#define GHCB_PROTOCOL_MIN      1ULL
 #define GHCB_PROTOCOL_MAX      1ULL
 #define GHCB_DEFAULT_USAGE     0ULL
 

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 2abf8a7..91105f5 100644 (file)
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -14,6 +14,15 @@
 #define has_cpuflag(f) boot_cpu_has(f)
 #endif
 
+/*
+ * Since feature negotiation related variables are set early in the boot
+ * process they must reside in the .data section so as not to be zeroed
+ * out when the .bss section is later cleared.
+ *
+ * GHCB protocol version negotiated with the hypervisor.
+ */
+static u16 ghcb_version __ro_after_init;
+
 static bool __init sev_es_check_cpu_features(void)
 {
        if (!has_cpuflag(X86_FEATURE_RDRAND)) {
@@ -51,10 +60,12 @@ static bool sev_es_negotiate_protocol(void)
        if (GHCB_MSR_INFO(val) != GHCB_MSR_SEV_INFO_RESP)
                return false;
 
-       if (GHCB_MSR_PROTO_MAX(val) < GHCB_PROTO_OUR ||
-           GHCB_MSR_PROTO_MIN(val) > GHCB_PROTO_OUR)
+       if (GHCB_MSR_PROTO_MAX(val) < GHCB_PROTOCOL_MIN ||
+           GHCB_MSR_PROTO_MIN(val) > GHCB_PROTOCOL_MAX)
                return false;
 
+       ghcb_version = min_t(size_t, GHCB_MSR_PROTO_MAX(val), GHCB_PROTOCOL_MAX);
+
        return true;
 }
 
@@ -127,7 +138,7 @@ enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb, bool set_ghcb_msr,
                                   u64 exit_info_1, u64 exit_info_2)
 {
        /* Fill in protocol and format specifiers */
-       ghcb->protocol_version = GHCB_PROTOCOL_MAX;
+       ghcb->protocol_version = ghcb_version;
        ghcb->ghcb_usage       = GHCB_DEFAULT_USAGE;
 
        ghcb_set_sw_exit_code(ghcb, exit_code);