[PATCH v7 09/45] x86/sev: Save the negotiated GHCB version

Brijesh Singh
2021-11-10T22:08:32Z

The SEV-ES guest calls the 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>
---
arch/x86/include/asm/sev.h | 2 +-
arch/x86/kernel/sev-shared.c | 17 ++++++++++++++---
2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ec060c433589..9b9c190e8c3b 100644
--- 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 2abf8a7d75e5..91105f5a02a8 100644
--- 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);
--
2.25.1