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Subject[PATCH v7 16/45] x86/sev: Register GHCB memory when SEV-SNP is active
Date
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@amd.com>
---
arch/x86/include/asm/sev.h | 2 +
arch/x86/kernel/cpu/common.c | 5 ++
arch/x86/kernel/head64.c | 3 +
arch/x86/kernel/sev.c | 116 ++++++++++++++++++++---------------
4 files changed, 77 insertions(+), 49 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index e37451849165..0df508374a35 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -122,6 +122,7 @@ static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)

return rc;
}
+void sev_snp_register_ghcb(void);
#else
static inline void sev_es_ist_enter(struct pt_regs *regs) { }
static inline void sev_es_ist_exit(void) { }
@@ -130,6 +131,7 @@ static inline void sev_es_nmi_complete(void) { }
static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs) { return 0; }
+static inline void sev_snp_register_ghcb(void) { }
#endif

#endif
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0083464de5e3..16b5667bbfdb 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -59,6 +59,7 @@
#include <asm/cpu_device_id.h>
#include <asm/uv/uv.h>
#include <asm/sigframe.h>
+#include <asm/sev.h>

#include "cpu.h"

@@ -1977,6 +1978,10 @@ void cpu_init_exception_handling(void)

load_TR_desc();

+ /* Register the GHCB before taking any VC exception */
+ if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
+ sev_snp_register_ghcb();
+
/* Finally load the IDT */
load_current_idt();
}
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 54bf0603002f..968105cec364 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -588,6 +588,9 @@ void early_setup_idt(void)

bringup_idt_descr.address = (unsigned long)bringup_idt_table;
native_load_idt(&bringup_idt_descr);
+
+ if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
+ sev_snp_register_ghcb();
}

/*
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 80a41e413cb8..30634e7e5c7b 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -158,55 +158,6 @@ void noinstr __sev_es_ist_exit(void)
this_cpu_write(cpu_tss_rw.x86_tss.ist[IST_INDEX_VC], *(unsigned long *)ist);
}

-/*
- * Nothing shall interrupt this code path while holding the per-CPU
- * GHCB. The backup GHCB is only for NMIs interrupting this path.
- *
- * Callers must disable local interrupts around it.
- */
-static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
-{
- struct sev_es_runtime_data *data;
- struct ghcb *ghcb;
-
- WARN_ON(!irqs_disabled());
-
- data = this_cpu_read(runtime_data);
- ghcb = &data->ghcb_page;
-
- if (unlikely(data->ghcb_active)) {
- /* GHCB is already in use - save its contents */
-
- if (unlikely(data->backup_ghcb_active)) {
- /*
- * Backup-GHCB is also already in use. There is no way
- * to continue here so just kill the machine. To make
- * panic() work, mark GHCBs inactive so that messages
- * can be printed out.
- */
- data->ghcb_active = false;
- data->backup_ghcb_active = false;
-
- instrumentation_begin();
- panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
- instrumentation_end();
- }
-
- /* Mark backup_ghcb active before writing to it */
- data->backup_ghcb_active = true;
-
- state->ghcb = &data->backup_ghcb;
-
- /* Backup GHCB content */
- *state->ghcb = *ghcb;
- } else {
- state->ghcb = NULL;
- data->ghcb_active = true;
- }
-
- return ghcb;
-}
-
static inline u64 sev_es_rd_ghcb_msr(void)
{
return __rdmsr(MSR_AMD64_SEV_ES_GHCB);
@@ -459,6 +410,55 @@ 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"

+/*
+ * Nothing shall interrupt this code path while holding the per-CPU
+ * GHCB. The backup GHCB is only for NMIs interrupting this path.
+ *
+ * Callers must disable local interrupts around it.
+ */
+static noinstr struct ghcb *__sev_get_ghcb(struct ghcb_state *state)
+{
+ struct sev_es_runtime_data *data;
+ struct ghcb *ghcb;
+
+ WARN_ON(!irqs_disabled());
+
+ data = this_cpu_read(runtime_data);
+ ghcb = &data->ghcb_page;
+
+ if (unlikely(data->ghcb_active)) {
+ /* GHCB is already in use - save its contents */
+
+ if (unlikely(data->backup_ghcb_active)) {
+ /*
+ * Backup-GHCB is also already in use. There is no way
+ * to continue here so just kill the machine. To make
+ * panic() work, mark GHCBs inactive so that messages
+ * can be printed out.
+ */
+ data->ghcb_active = false;
+ data->backup_ghcb_active = false;
+
+ instrumentation_begin();
+ panic("Unable to handle #VC exception! GHCB and Backup GHCB are already in use");
+ instrumentation_end();
+ }
+
+ /* Mark backup_ghcb active before writing to it */
+ data->backup_ghcb_active = true;
+
+ state->ghcb = &data->backup_ghcb;
+
+ /* Backup GHCB content */
+ *state->ghcb = *ghcb;
+ } else {
+ state->ghcb = NULL;
+ data->ghcb_active = true;
+ }
+
+ return ghcb;
+}
+
static noinstr void __sev_put_ghcb(struct ghcb_state *state)
{
struct sev_es_runtime_data *data;
@@ -650,6 +650,10 @@ 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 (cc_platform_has(CC_ATTR_SEV_SNP))
+ snp_register_ghcb_early(__pa(&boot_ghcb_page));
+
return true;
}

@@ -741,6 +745,20 @@ static void __init init_ghcb(int cpu)
data->backup_ghcb_active = false;
}

+void sev_snp_register_ghcb(void)
+{
+ struct sev_es_runtime_data *data;
+ struct ghcb *ghcb;
+
+ if (!cc_platform_has(CC_ATTR_SEV_SNP))
+ return;
+
+ data = this_cpu_read(runtime_data);
+ ghcb = &data->ghcb_page;
+
+ snp_register_ghcb_early(__pa(ghcb));
+}
+
void __init sev_es_init_vc_handling(void)
{
int cpu;
--
2.25.1
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