linux-kernel - [RFC PATCH 03/12] x86/sev: Save and print negotiated GHCB protocol version

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Date:   Mon,  5 Jul 2021 10:24:34 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Joerg Roedel <joro@...tes.org>, Joerg Roedel <jroedel@...e.de>,
        hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: [RFC PATCH 03/12] x86/sev: Save and print negotiated GHCB protocol version

From: Joerg Roedel <jroedel@...e.de>

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

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/boot/compressed/sev.c |  2 +-
 arch/x86/kernel/sev-shared.c   | 22 +++++++++++++++++++++-
 arch/x86/kernel/sev.c          | 13 ++++++++++++-
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 670e998fe930..1a2e49730f8b 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -121,7 +121,7 @@ static enum es_result vc_read_mem(struct es_em_ctxt *ctxt,
 
 static bool early_setup_sev_es(void)
 {
-	if (!sev_es_negotiate_protocol())
+	if (!sev_es_negotiate_protocol(NULL))
 		sev_es_terminate(GHCB_SEV_ES_REASON_PROTOCOL_UNSUPPORTED);
 
 	if (set_page_decrypted((unsigned long)&boot_ghcb_page))
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 9f90f460a28c..73eeb5897d16 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -14,6 +14,20 @@
 #define has_cpuflag(f)	boot_cpu_has(f)
 #endif
 
+/*
+ * struct sev_ghcb_protocol_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 sev_ghcb_protocol_info {
+	unsigned int hv_proto_min;
+	unsigned int hv_proto_max;
+	unsigned int vm_proto;
+};
+
 static bool __init sev_es_check_cpu_features(void)
 {
 	if (!has_cpuflag(X86_FEATURE_RDRAND)) {
@@ -42,7 +56,7 @@ static void __noreturn sev_es_terminate(unsigned int reason)
 		asm volatile("hlt\n" : : : "memory");
 }
 
-static bool sev_es_negotiate_protocol(void)
+static bool sev_es_negotiate_protocol(struct sev_ghcb_protocol_info *info)
 {
 	u64 val;
 
@@ -58,6 +72,12 @@ static bool sev_es_negotiate_protocol(void)
 	    GHCB_MSR_PROTO_MIN(val) > GHCB_PROTO_OUR)
 		return false;
 
+	if (info) {
+		info->hv_proto_min = GHCB_MSR_PROTO_MIN(val);
+		info->hv_proto_max = GHCB_MSR_PROTO_MAX(val);
+		info->vm_proto	   = GHCB_PROTO_OUR;
+	}
+
 	return true;
 }
 
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a6895e440bc3..8084bfd7cce1 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -495,6 +495,9 @@ static enum es_result vc_slow_virt_to_phys(struct ghcb *ghcb, struct es_em_ctxt
 /* Include code shared with pre-decompression boot stage */
 #include "sev-shared.c"
 
+/* Negotiated GHCB protocol version */
+static struct sev_ghcb_protocol_info ghcb_protocol_info __ro_after_init;
+
 static noinstr void __sev_put_ghcb(struct ghcb_state *state)
 {
 	struct sev_es_runtime_data *data;
@@ -665,7 +668,7 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 static bool __init sev_es_setup_ghcb(void)
 {
 	/* First make sure the hypervisor talks a supported protocol. */
-	if (!sev_es_negotiate_protocol())
+	if (!sev_es_negotiate_protocol(&ghcb_protocol_info))
 		return false;
 
 	/*
@@ -794,6 +797,14 @@ 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_protocol_info.hv_proto_min, ghcb_protocol_info.hv_proto_max);
+	pr_info("Using GHCB protocol version %u\n", ghcb_protocol_info.vm_proto);
 }
 
 static void __init vc_early_forward_exception(struct es_em_ctxt *ctxt)
-- 
2.31.1