diff mbox series

[v8,11/40] x86/sev: Register GHCB memory when SEV-SNP is active

Message ID 20211210154332.11526-12-brijesh.singh@amd.com
State New
Headers show
Series Add AMD Secure Nested Paging (SEV-SNP) Guest Support | expand

Commit Message

Brijesh Singh Dec. 10, 2021, 3:43 p.m. UTC 
The SEV-SNP guest is required by the GHCB spec to register the GHCB's
Guest Physical Address (GPA). 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".

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 arch/x86/include/asm/sev.h   |   2 +
 arch/x86/kernel/cpu/common.c |   4 ++
 arch/x86/kernel/head64.c     |   1 +
 arch/x86/kernel/sev-shared.c |   2 +-
 arch/x86/kernel/sev.c        | 120 ++++++++++++++++++++---------------
 5 files changed, 77 insertions(+), 52 deletions(-)

Comments

Borislav Petkov Dec. 22, 2021, 1:16 p.m. UTC | #1 
On Fri, Dec 10, 2021 at 09:43:03AM -0600, Brijesh Singh wrote:
> @@ -652,7 +652,7 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
>   * This function runs on the first #VC exception after the kernel
>   * switched to virtual addresses.
>   */
> -static bool __init sev_es_setup_ghcb(void)
> +static bool __init setup_ghcb(void)
>  {
>  	/* First make sure the hypervisor talks a supported protocol. */
>  	if (!sev_es_negotiate_protocol())

Ok, let me stare at this for a while:

This gets called by handle_vc_boot_ghcb() which gets set at build time:

arch/x86/kernel/head_64.S:372:SYM_DATA(initial_vc_handler,      .quad handle_vc_boot_ghcb)

initial_vc_handler() gets called by vc_boot_ghcb() which gets set in

early_setup_idt()

and that function already does sev_snp_register_ghcb().

So why don't you concentrate the work setup_ghcb() does before the first
#VC and call it in early_setup_idt(), before the IDT is set?

And then you get rid of yet another setup-at-first-use case?

Thx.
Brijesh Singh Dec. 22, 2021, 3:16 p.m. UTC | #2 
On 12/22/21 7:16 AM, Borislav Petkov wrote:
> On Fri, Dec 10, 2021 at 09:43:03AM -0600, Brijesh Singh wrote:
>> @@ -652,7 +652,7 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
>>    * This function runs on the first #VC exception after the kernel
>>    * switched to virtual addresses.
>>    */
>> -static bool __init sev_es_setup_ghcb(void)
>> +static bool __init setup_ghcb(void)
>>   {
>>   	/* First make sure the hypervisor talks a supported protocol. */
>>   	if (!sev_es_negotiate_protocol())
> 
> Ok, let me stare at this for a while:
> 
> This gets called by handle_vc_boot_ghcb() which gets set at build time:
> 
> arch/x86/kernel/head_64.S:372:SYM_DATA(initial_vc_handler,      .quad handle_vc_boot_ghcb)
> 
> initial_vc_handler() gets called by vc_boot_ghcb() which gets set in
> 
> early_setup_idt()
> 
> and that function already does sev_snp_register_ghcb().
> 
> So why don't you concentrate the work setup_ghcb() does before the first
> #VC and call it in early_setup_idt(), before the IDT is set?
> 
> And then you get rid of yet another setup-at-first-use case?
> 

I was following the existing SEV-ES implementation in which GHCB is 
setup on first #VC. But recently you recommended to move the setup 
outside of the VC handler for the decompression path and I was going to 
do the same for the kernel proper. I have tried moving the GHCB setup 
outside and it seems to be working okay with me (a limited testing so 
far). I will check Jorge to see if there was any reason for doing the 
GHCB setup inside the VC for the SEV-ES case.
diff mbox series

Patch

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 0663642d6199..1146e8920b03 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"
 
@@ -1988,6 +1989,9 @@  void cpu_init_exception_handling(void)
 
 	load_TR_desc();
 
+	/* Register the GHCB before taking any VC exception */
+	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 b01f64e8389b..fa02402dcb9b 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -588,6 +588,7 @@  void early_setup_idt(void)
 
 	bringup_idt_descr.address = (unsigned long)bringup_idt_table;
 	native_load_idt(&bringup_idt_descr);
+	sev_snp_register_ghcb();
 }
 
 /*
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index e9ff13cd90b0..3aaef1a18ffe 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -68,7 +68,7 @@  static u64 get_hv_features(void)
 	return GHCB_MSR_HV_FT_RESP_VAL(val);
 }
 
-static void __maybe_unused snp_register_ghcb_early(unsigned long paddr)
+static void snp_register_ghcb_early(unsigned long paddr)
 {
 	unsigned long pfn = paddr >> PAGE_SHIFT;
 	u64 val;
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a0cada8398a4..17ad603f62da 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -162,55 +162,6 @@  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);
@@ -484,6 +435,55 @@  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;
@@ -652,7 +652,7 @@  static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
  * This function runs on the first #VC exception after the kernel
  * switched to virtual addresses.
  */
-static bool __init sev_es_setup_ghcb(void)
+static bool __init setup_ghcb(void)
 {
 	/* First make sure the hypervisor talks a supported protocol. */
 	if (!sev_es_negotiate_protocol())
@@ -667,6 +667,10 @@  static bool __init sev_es_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;
 }
 
@@ -758,6 +762,20 @@  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;
@@ -1400,7 +1418,7 @@  bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
 	enum es_result result;
 
 	/* Do initial setup or terminate the guest */
-	if (unlikely(boot_ghcb == NULL && !sev_es_setup_ghcb()))
+	if (unlikely(boot_ghcb == NULL && !setup_ghcb()))
 		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
 
 	vc_ghcb_invalidate(boot_ghcb);