The SEV-SNP guest is required to perform GHCB GPA registration. This is
because the hypervisor may prefer that a guest use a consistent and/or
specific GPA for the GHCB associated with a vCPU. For more information,
see the GHCB specification section GHCB GPA Registration.
During the boot, init_ghcb() allocates a per-cpu GHCB page. On very first
VC exception, the exception handler switch to using the per-cpu GHCB page
allocated during the init_ghcb(). The GHCB page must be registered in
the current vcpu context.
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
arch/x86/kernel/sev-internal.h | 12 ++++++++++++
arch/x86/kernel/sev.c | 29 +++++++++++++++++++++++++++++
2 files changed, 41 insertions(+)
create mode 100644 arch/x86/kernel/sev-internal.h
diff --git a/arch/x86/kernel/sev-internal.h b/arch/x86/kernel/sev-internal.h
new file mode 100644
index 000000000000..0fb7324803b4
--- /dev/null
+++ b/arch/x86/kernel/sev-internal.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Forward declarations for sev-shared.c
+ *
+ * Author: Brijesh Singh <brijesh.singh@xxxxxxx>
+ */
+
+#ifndef __X86_SEV_INTERNAL_H__
+
+static void snp_register_ghcb_early(unsigned long paddr);
+
+#endif /* __X86_SEV_INTERNAL_H__ */
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 504169f1966b..c7ff60b55bde 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -31,6 +31,8 @@
#include <asm/smp.h>
#include <asm/cpu.h>
+#include "sev-internal.h"
+
#define DR7_RESET_VALUE 0x400
/* For early boot hypervisor communication in SEV-ES enabled guests */
@@ -87,6 +89,13 @@ struct sev_es_runtime_data {
* is currently unsupported in SEV-ES guests.
*/
unsigned long dr7;
+
+ /*
+ * SEV-SNP requires that the GHCB must be registered before using it.
+ * The flag below will indicate whether the GHCB is registered, if its
+ * not registered then sev_es_get_ghcb() will perform the registration.
+ */
+ bool snp_ghcb_registered;
};
struct ghcb_state {
@@ -194,6 +203,17 @@ void noinstr __sev_es_ist_exit(void)
this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
}
+static void snp_register_ghcb(struct sev_es_runtime_data *data, unsigned long paddr)
+{
+ if (data->snp_ghcb_registered)
+ return;
+
+ snp_register_ghcb_early(paddr);
+
+ data->snp_ghcb_registered = true;
+}
+
+
/*
* Nothing shall interrupt this code path while holding the per-CPU
* GHCB. The backup GHCB is only for NMIs interrupting this path.
@@ -240,6 +260,10 @@ static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
data->ghcb_active = true;
}
+ /* SEV-SNP guest requires that GHCB must be registered. */
+ if (sev_feature_enabled(SEV_SNP))
+ snp_register_ghcb(data, __pa(ghcb));
+
return ghcb;
}
@@ -684,6 +708,10 @@ static bool __init setup_ghcb(void)
/* Alright - Make the boot-ghcb public */
boot_ghcb = &boot_ghcb_page;
+ /* SEV-SNP guest requires that GHCB GPA must be registered. */
+ if (sev_feature_enabled(SEV_SNP))
+ snp_register_ghcb_early(__pa(&boot_ghcb_page));
+
return true;
}
@@ -773,6 +801,7 @@ static void __init init_ghcb(int cpu)
data->ghcb_active = false;
data->backup_ghcb_active = false;
+ data->snp_ghcb_registered = false;
}
void __init sev_es_init_vc_handling(void)
--
2.17.1
