[PATCH v3 02/10] x86/sev: Save and print negotiated GHCB protocol version

Joerg Roedel
2022-01-27T10:11:29Z

Save the results of the GHCB protocol negotiation into a data structure
and print information about versions supported and used to the kernel
log.

This is useful for debugging kexec issues in SEV-ES guests down the
road to quickly spot whether kexec is supported on the given host.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
arch/x86/include/asm/sev.h | 4 ++--
arch/x86/kernel/sev-shared.c | 36 ++++++++++++++++++++++++++++++++++--
arch/x86/kernel/sev.c | 8 ++++++++
3 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index ec060c433589..17b75f6ee11a 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -12,8 +12,8 @@
#include <asm/insn.h>
#include <asm/sev-common.h>

-#define GHCB_PROTO_OUR 0x0001UL
-#define GHCB_PROTOCOL_MAX 1ULL
+#define GHCB_PROTOCOL_MIN 1ULL
+#define GHCB_PROTOCOL_MAX 2ULL
#define GHCB_DEFAULT_USAGE 0ULL

#define VMGEXIT() { asm volatile("rep; vmmcall\n\r"); }
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index ce987688bbc0..60ca7dd64d64 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -14,6 +14,23 @@
#define has_cpuflag(f) boot_cpu_has(f)
#endif

+/*
+ * struct ghcb_info - Used to return GHCB protocol
+ * negotiation details.
+ *
+ * @hv_proto_min: Minimum GHCB protocol version supported by Hypervisor
+ * @hv_proto_max: Maximum GHCB protocol version supported by Hypervisor
+ * @vm_proto: Protocol version the VM (this kernel) will use
+ */
+struct ghcb_info {
+ unsigned int hv_proto_min;
+ unsigned int hv_proto_max;
+ unsigned int vm_proto;
+};
+
+/* Negotiated GHCB protocol version */
+static struct ghcb_info ghcb_info __ro_after_init;
+
static bool __init sev_es_check_cpu_features(void)
{
if (!has_cpuflag(X86_FEATURE_RDRAND)) {
@@ -44,6 +61,7 @@ static void __noreturn sev_es_terminate(unsigned int reason)

static bool sev_es_negotiate_protocol(void)
{
+ unsigned int protocol;
u64 val;

/* Do the GHCB protocol version negotiation */
@@ -54,10 +72,24 @@ 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)
+ /* Sanity check untrusted input */
+ if (GHCB_MSR_PROTO_MIN(val) > GHCB_MSR_PROTO_MAX(val))
return false;

+ /* Use maximum supported protocol version */
+ protocol = min_t(unsigned int, GHCB_MSR_PROTO_MAX(val), GHCB_PROTOCOL_MAX);
+
+ /*
+ * Hypervisor does not support any protocol version required for this
+ * kernel.
+ */
+ if (protocol < GHCB_MSR_PROTO_MIN(val))
+ return false;
+
+ ghcb_info.hv_proto_min = GHCB_MSR_PROTO_MIN(val);
+ ghcb_info.hv_proto_max = GHCB_MSR_PROTO_MAX(val);
+ ghcb_info.vm_proto = protocol;
+
return true;
}

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index e6d316a01fdd..8a4317fa699a 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -779,6 +779,14 @@ void __init sev_es_init_vc_handling(void)

/* Secondary CPUs use the runtime #VC handler */
initial_vc_handler = (unsigned long)kernel_exc_vmm_communication;
+
+ /*
+ * Print information about supported and negotiated GHCB protocol
+ * versions.
+ */
+ pr_info("Hypervisor GHCB protocol version support: min=%u max=%u\n",
+ ghcb_info.hv_proto_min, ghcb_info.hv_proto_max);
+ pr_info("Using GHCB protocol version %u\n", ghcb_info.vm_proto);
}

static void __init vc_early_forward_exception(struct es_em_ctxt *ctxt)
--
2.34.1