[PATCH v3 75/75] x86/efi: Add GHCB mappings when SEV-ES is active

[Joerg Roedel]

From: Tom Lendacky <thomas.lendacky@xxxxxxx>

Calling down to EFI runtime services can result in the firmware performing
VMGEXIT calls. The firmware is likely to use the GHCB of the OS (e.g., for
setting EFI variables), so each GHCB in the system needs to be identity
mapped in the EFI page tables, as unencrypted, to avoid page faults.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
[ jroedel@xxxxxxx: Moved GHCB mapping loop to sev-es.c ]
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
 arch/x86/boot/compressed/sev-es.c |  1 +
 arch/x86/include/asm/sev-es.h     |  5 +++++
 arch/x86/kernel/sev-es.c          | 25 +++++++++++++++++++++++++
 arch/x86/platform/efi/efi_64.c    | 10 ++++++++++
 4 files changed, 41 insertions(+)

diff --git a/arch/x86/boot/compressed/sev-es.c b/arch/x86/boot/compressed/sev-es.c
index 12a5d918d837..30b2cebf5fed 100644
--- a/arch/x86/boot/compressed/sev-es.c
+++ b/arch/x86/boot/compressed/sev-es.c
@@ -12,6 +12,7 @@
  */
 #include "misc.h"
 
+#include <asm/pgtable_types.h>
 #include <asm/sev-es.h>
 #include <asm/trap_defs.h>
 #include <asm/msr-index.h>
diff --git a/arch/x86/include/asm/sev-es.h b/arch/x86/include/asm/sev-es.h
index a242d16727f1..ce9a197bf958 100644
--- a/arch/x86/include/asm/sev-es.h
+++ b/arch/x86/include/asm/sev-es.h
@@ -87,6 +87,7 @@ void sev_es_nmi_enter(void);
 void sev_es_nmi_exit(void);
 int sev_es_setup_ap_jump_table(struct real_mode_header *rmh);
 void sev_es_nmi_complete(void);
+int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
 #else /* CONFIG_AMD_MEM_ENCRYPT */
 static inline const char *vc_stack_name(enum stack_type type)
 {
@@ -97,6 +98,10 @@ static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh)
 	return 0;
 }
 static inline void sev_es_nmi_complete(void) { }
+static inline int sev_es_efi_map_ghcbs(pgd_t *pgd)
+{
+	return 0;
+}
 #endif /* CONFIG_AMD_MEM_ENCRYPT*/
 
 #endif
diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index eef6e2196ef4..3b62714723b5 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -422,6 +422,31 @@ int sev_es_setup_ap_jump_table(struct real_mode_header *rmh)
 	return 0;
 }
 
+int __init sev_es_efi_map_ghcbs(pgd_t *pgd)
+{
+	struct sev_es_runtime_data *data;
+	unsigned long address, pflags;
+	int cpu;
+	u64 pfn;
+
+	if (!sev_es_active())
+		return 0;
+
+	pflags = _PAGE_NX | _PAGE_RW;
+
+	for_each_possible_cpu(cpu) {
+		data = per_cpu(runtime_data, cpu);
+
+		address = __pa(&data->ghcb_page);
+		pfn = address >> PAGE_SHIFT;
+
+		if (kernel_map_pages_in_pgd(pgd, pfn, address, 1, pflags))
+			return 1;
+	}
+
+	return 0;
+}
+
 static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
 {
 	struct pt_regs *regs = ctxt->regs;
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index c5e393f8bb3f..004a18853dd3 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -48,6 +48,7 @@
 #include <asm/realmode.h>
 #include <asm/time.h>
 #include <asm/pgalloc.h>
+#include <asm/sev-es.h>
 
 /*
  * We allocate runtime services regions top-down, starting from -4G, i.e.
@@ -239,6 +240,15 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 		return 1;
 	}
 
+	/*
+	 * When SEV-ES is active, the GHCB as set by the kernel will be used
+	 * by firmware. Create a 1:1 unencrypted mapping for each GHCB.
+	 */
+	if (sev_es_efi_map_ghcbs(pgd)) {
+		pr_err("Failed to create 1:1 mapping for the GHCBs!\n");
+		return 1;
+	}
+
 	/*
 	 * When making calls to the firmware everything needs to be 1:1
 	 * mapped and addressable with 32-bit pointers. Map the kernel
-- 
2.17.1