[PATCH v6 02/10] x86/sev: Save and print negotiated GHCB protocol version

vsntk18
2024-06-10T10:21:28Z

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>
Signed-off-by: Vasant Karasulli <vkarasulli@suse.de>
---
arch/x86/kernel/sev-shared.c | 33 +++++++++++++++++++++++++++++++--
arch/x86/kernel/sev.c | 8 ++++++++
2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index b4f8fa0f722c..f5717eddf75b 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -23,6 +23,23 @@
#define sev_printk_rtl(fmt, ...)
#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;
+
/* I/O parameters for CPUID-related helpers */
struct cpuid_leaf {
u32 fn;
@@ -159,12 +176,24 @@ 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_PROTOCOL_MIN ||
- GHCB_MSR_PROTO_MIN(val) > GHCB_PROTOCOL_MAX)
+ /* Sanity check untrusted input */
+ if (GHCB_MSR_PROTO_MIN(val) > GHCB_MSR_PROTO_MAX(val))
return false;

+ /* Use maximum supported protocol version */
ghcb_version = min_t(size_t, GHCB_MSR_PROTO_MAX(val), GHCB_PROTOCOL_MAX);

+ /*
+ * Hypervisor does not support any protocol version required for this
+ * kernel.
+ */
+ if (ghcb_version < 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 = ghcb_version;
+
return true;
}

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 3342ed58e168..f0d87549b1e1 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1399,6 +1399,14 @@ 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