Add SEV-SNP CipherTextHiding feature support

From: Ashish Kalra <[email protected]>

The FEATURE_INFO command provides host and guests a programmatic means to learn about the supported features of the currently loaded firmware. FEATURE_INFO command leverages the same mechanism as the CPUID instruction. Instead of using the CPUID instruction to retrieve Fn8000_0024, software can use FEATURE_INFO.

Host/Hypervisor would use the FEATURE_INFO command, while guests would actually issue the CPUID instruction.

The hypervisor can provide Fn8000_0024 values to the guest via the CPUID page in SNP_LAUNCH_UPDATE. As with all CPUID output recorded in that page, the hypervisor can filter Fn8000_0024. The firmware will examine Fn8000_0024 and apply its CPUID policy.

During CCP module initialization, after firmware update, the SNP platform status and feature information from CPUID 0x8000_0024, sub-function 0, are cached in the sev_device structure.

Signed-off-by Ashish Kalra <[email protected]>

---
 drivers/crypto/ccp/sev-dev.c | 47 ++++++++++++++++++++++++++++++++++++
 drivers/crypto/ccp/sev-dev.h |  3 +++
 include/linux/psp-sev.h      | 29 ++++++++++++++++++++++
 3 files changed, 79 insertions(+)

drivers/crypto/ccp/sev-dev.c +11 -0

index b08db412f752..f4f8a8905115 100644
@@ -232,6 +232,7 @@ static int sev_cmd_buffer_len(int cmd)
 	case SEV_CMD_SNP_GUEST_REQUEST:		return sizeof(struct sev_data_snp_guest_request);
 	case SEV_CMD_SNP_CONFIG:		return sizeof(struct sev_user_data_snp_config);
 	case SEV_CMD_SNP_COMMIT:		return sizeof(struct sev_data_snp_commit);
+	case SEV_CMD_SNP_FEATURE_INFO:		return sizeof(struct snp_feature_info);
 	default:				return 0;
 	}
 

@@ -1072,6 +1073,50 @@ static void snp_set_hsave_pa(void *arg)
 	wrmsrq(MSR_VM_HSAVE_PA, 0);
 }
 
+static void snp_get_platform_data(void)
+{
+	struct sev_device *sev = psp_master->sev_data;
+	struct sev_data_snp_feature_info snp_feat_info;
+	struct snp_feature_info *feat_info;
+	struct sev_data_snp_addr buf;
+	int error = 0, rc;
+
+	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
+		return;

drivers/crypto/ccp/sev-dev.c +1 -0

+
 	return;
 
 err:

drivers/crypto/ccp/sev-dev.h +3 -0

index 3e4e5574e88a..1c1a51e52d2b 100644
@@ -57,6 +57,9 @@ struct sev_device {
 	bool cmd_buf_backup_active;
 
 	bool snp_initialized;
+
+	struct sev_user_data_snp_status snp_plat_status;
+	struct snp_feature_info feat_info;
 };
 
 int sev_dev_init(struct psp_device *psp);

include/linux/psp-sev.h +29 -0

index 0b3a36bdaa90..0149d4a6aceb 100644
@@ -107,6 +107,7 @@ enum sev_cmd {
 	SEV_CMD_SNP_DOWNLOAD_FIRMWARE_EX = 0x0CA,
 	SEV_CMD_SNP_COMMIT		= 0x0CB,
 	SEV_CMD_SNP_VLEK_LOAD		= 0x0CD,
+	SEV_CMD_SNP_FEATURE_INFO	= 0x0CE,
 
 	SEV_CMD_MAX,
 };

@@ -812,6 +813,34 @@ struct sev_data_snp_commit {
 	u32 len;
 } __packed;
 
+/**
+ * struct sev_data_snp_feature_info - SEV_SNP_FEATURE_INFO structure
+ *
+ * @length: len of the command buffer read by the PSP
+ * @ecx_in: subfunction index
+ * @feature_info_paddr : SPA of the FEATURE_INFO structure
+ */
+struct sev_data_snp_feature_info {
+	u32 length;
+	u32 ecx_in;
+	u64 feature_info_paddr;
+} __packed;
+
+/**
+ * struct feature_info - FEATURE_INFO structure
+ *
+ * @eax: output of SNP_FEATURE_INFO command
+ * @ebx: output of SNP_FEATURE_INFO command
+ * @ecx: output of SNP_FEATURE_INFO command
+ * #edx: output of SNP_FEATURE_INFO command
+ */
+struct snp_feature_info {
+	u32 eax;
+	u32 ebx;
+	u32 ecx;
+	u32 edx;
+} __packed;
+
 #ifdef CONFIG_CRYPTO_DEV_SP_PSP
 
 /**

drivers/crypto/ccp/sev- renamed from drivers/crypto/ccp/sev-dev.c +0 -0

dev.c
index b08db412f752..f4f8a8905115 100644

drivers/crypto/ccp/sev-dev.c +1 -0

@@ -232,6 +232,7 @@ static int sev_cmd_buffer_len(int cmd)
 	case SEV_CMD_SNP_GUEST_REQUEST:		return
 sizeof(struct sev_data_snp_guest_request);
 	case SEV_CMD_SNP_CONFIG:		return sizeof(struct
 sev_user_data_snp_config);
 	case SEV_CMD_SNP_COMMIT:		return sizeof(struct
 sev_data_snp_commit);
+	case SEV_CMD_SNP_FEATURE_INFO:		return sizeof(struct

snp_feature_info);

drivers/crypto/ccp/sev-dev.c +29 -0

 	default:				return 0;
 	}

@@ -1072,6 +1073,50 @@ static void snp_set_hsave_pa(void *arg)
 	wrmsrq(MSR_VM_HSAVE_PA, 0);
 }
 
+static void snp_get_platform_data(void)
+{
+	struct sev_device *sev = psp_master->sev_data;
+	struct sev_data_snp_feature_info snp_feat_info;
+	struct snp_feature_info *feat_info;
+	struct sev_data_snp_addr buf;
+	int error = 0, rc;
+
+	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
+		return;
+
+	/*
+	 * The output buffer must be firmware page if SEV-SNP is
+	 * initialized.
+	 */
+	if (sev->snp_initialized)
+		return;
+
+	buf.address = __psp_pa(&sev->snp_plat_status);
+	rc = __sev_do_cmd_locked(SEV_CMD_SNP_PLATFORM_STATUS, &buf,
 &error);
+
+	/*
+	 * Do feature discovery of the currently loaded firmware,
+	 * and cache feature information from CPUID 0x8000_0024,
+	 * sub-function 0.
+	 */
+	if (!rc && sev->snp_plat_status.feature_info) {
+		/*
+		 * Use dynamically allocated structure for the

SNP_FEATURE_INFO

drivers/crypto/ccp/sev-dev.c +1 -0

+		 * command to handle any alignment and page boundary

check

From: Ashish Kalra <[email protected]>

Ciphertext hiding needs to be enabled on SNP_INIT_EX.

Add two new arguments to sev_platform_init_args to allow KVM module to specify during SNP initialization if CipherTextHiding feature is to be enabled and the maximum ASID usable for an SEV-SNP guest when CipherTextHiding feature is enabled.

Add new API interface to indicate if SEV-SNP CipherTextHiding feature is supported and enabled in the Platform/BIOS.

Signed-off-by Ashish Kalra <[email protected]>

---
 drivers/crypto/ccp/sev-dev.c | 31 ++++++++++++++++++++++++++++---
 include/linux/psp-sev.h      | 18 ++++++++++++++++--
 2 files changed, 44 insertions(+), 5 deletions(-)

drivers/crypto/ccp/sev-dev.c +0 -0

index f4f8a8905115..ca4b156598de 100644

drivers/crypto/ccp/sev-dev.c +12 -3

+}
+EXPORT_SYMBOL_GPL(is_sev_snp_ciphertext_hiding_supported);
+
 static void snp_get_platform_data(void)
 {
 	struct sev_device *sev = psp_master->sev_data;

@@ -1147,7 +1166,7 @@ static int snp_filter_reserved_mem_regions(struct resource *rs, void *arg)
 	return 0;
 }
 
-static int __sev_snp_init_locked(int *error)
+static int __sev_snp_init_locked(int *error, bool cipher_text_hiding_en, unsigned int snp_max_snp_asid)
 {
 	struct psp_device *psp = psp_master;
 	struct sev_data_snp_init_ex data;

@@ -1208,6 +1227,12 @@ static int __sev_snp_init_locked(int *error)
 		}
 
 		memset(&data, 0, sizeof(data));
+
+		if (cipher_text_hiding_en) {
+			data.ciphertext_hiding_en = 1;
+			data.max_snp_asid = snp_max_snp_asid;
+		}
+
 		data.init_rmp = 1;
 		data.list_paddr_en = 1;
 		data.list_paddr = __psp_pa(snp_range_list);

@@ -1392,7 +1417,7 @@ static int _sev_platform_init_locked(struct sev_platform_init_args *args)
 	if (sev->state == SEV_STATE_INIT)
 		return 0;
 
-	rc = __sev_snp_init_locked(&args->error);
+	rc = __sev_snp_init_locked(&args->error, args->cipher_text_hiding_en, args->snp_max_snp_asid);
 	if (rc && rc != -ENODEV)
 		return rc;
 

@@ -1475,7 +1500,7 @@ static int snp_move_to_init_state(struct sev_issue_cmd *argp, bool *shutdown_req
 {
 	int error, rc;
 
-	rc = __sev_snp_init_locked(&error);
+	rc = __sev_snp_init_locked(&error, false, 0);
 	if (rc) {
 		argp->error = SEV_RET_INVALID_PLATFORM_STATE;
 		return rc;

include/linux/psp-sev.h +5 -2

index 0149d4a6aceb..af45e3e372f5 100644
@@ -746,10 +746,13 @@ struct sev_data_snp_guest_request {
 struct sev_data_snp_init_ex {
 	u32 init_rmp:1;
 	u32 list_paddr_en:1;
-	u32 rsvd:30;
+	u32 rapl_dis:1;
+	u32 ciphertext_hiding_en:1;
+	u32 rsvd:28;
 	u32 rsvd1;
 	u64 list_paddr;
-	u8  rsvd2[48];
+	u16 max_snp_asid;
+	u8  rsvd2[46];
 } __packed;
 
 /**

include/linux/psp-sev.h +10 -0

+ *  enabled
+ *  @snp_max_snp_asid: maximum ASID usable for SEV-SNP guest if
+ *  CipherTextHiding is enabled
  */
 struct sev_platform_init_args {
 	int error;
 	bool probe;
+	bool cipher_text_hiding_en;
+	unsigned int snp_max_snp_asid;
 };
 
 /**

@@ -841,6 +850,8 @@ struct snp_feature_info {
 	u32 edx;
 } __packed;
 
+#define SNP_CIPHER_TEXT_HIDING_SUPPORTED	BIT(3)
+
 #ifdef CONFIG_CRYPTO_DEV_SP_PSP
 
 /**

@@ -984,6 +995,7 @@ void *psp_copy_user_blob(u64 uaddr, u32 len);
 void *snp_alloc_firmware_page(gfp_t mask);
 void snp_free_firmware_page(void *addr);
 void sev_platform_shutdown(void);
+bool is_sev_snp_ciphertext_hiding_supported(void);
 
 #else	/* !CONFIG_CRYPTO_DEV_SP_PSP */
 

@@ -1020,6 +1032,8 @@ static inline void snp_free_firmware_page(void *addr) { }
 
 static inline void sev_platform_shutdown(void) { }
 
+static inline bool is_sev_snp_ciphertext_hiding_supported(void) { return FALSE; }
+
 #endif	/* CONFIG_CRYPTO_DEV_SP_PSP */
 
 #endif	/* __PSP_SEV_H__ */

From: Ashish Kalra <[email protected]>

Ciphertext hiding prevents host accesses from reading the ciphertext of SNP guest private memory. Instead of reading ciphertext, the host reads will see constant default values (0xff).

Ciphertext hiding separates the ASID space into SNP guest ASIDs and host ASIDs.

All SNP active guests must have an ASID less than or equal to MAX_SNP_ASID provided to the SNP_INIT_EX command. All SEV-legacy guests (SEV and SEV-ES) must be greater than MAX_SNP_ASID.

This patch-set adds two new module parameters to the KVM module, first

to enable CipherTextHiding support and a user configurable MAX_SNP_ASID to define the system-wide maximum SNP ASID value. If this value is not set, then the ASID space is equally divided between SEV-SNP and SEV-ES guests.

Signed-off-by Ashish Kalra <[email protected]>

---
 arch/x86/kvm/svm/sev.c | 50 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

arch/x86/kvm/svm/sev.c +0 -0

index 7a156ba07d1f..a905f755312a 100644

arch/x86/kvm/svm/sev.c +3 -1

 #define AP_RESET_HOLD_NONE		0
 #define AP_RESET_HOLD_NAE_EVENT		1
 #define AP_RESET_HOLD_MSR_PROTO		2

@@ -85,6 +93,8 @@ static DEFINE_MUTEX(sev_bitmap_lock);
 unsigned int max_sev_asid;
 static unsigned int min_sev_asid;
 static unsigned long sev_me_mask;
+static unsigned int snp_max_snp_asid;
+static bool snp_cipher_text_hiding;
 static unsigned int nr_asids;
 static unsigned long *sev_asid_bitmap;
 static unsigned long *sev_reclaim_asid_bitmap;

@@ -171,7 +181,7 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
 	misc_cg_uncharge(type, sev->misc_cg, 1);
 }
 
-static int sev_asid_new(struct kvm_sev_info *sev)
+static int sev_asid_new(struct kvm_sev_info *sev, unsigned long vm_type)
 {
 	/*
 	 * SEV-enabled guests must use asid from min_sev_asid to max_sev_asid.

arch/x86/kvm/svm/sev.c +3 -1

@@ -3040,14 +3074,18 @@ void __init sev_hardware_setup(void)
 								       "unusable" :
 								       "disabled",
 			min_sev_asid, max_sev_asid);
-	if (boot_cpu_has(X86_FEATURE_SEV_ES))
+	if (boot_cpu_has(X86_FEATURE_SEV_ES)) {
+		if (snp_max_snp_asid >= (min_sev_asid - 1))
+			sev_es_supported = false;
 		pr_info("SEV-ES %s (ASIDs %u - %u)\n",

arch/x86/kvm/svm/sev.c +2 -0

 	sev_enabled = sev_supported;
 	sev_es_enabled = sev_es_supported;

@@ -3068,6 +3106,8 @@ void __init sev_hardware_setup(void)
 	 * Do both SNP and SEV initialization at KVM module load.
 	 */
 	init_args.probe = true;
+	init_args.cipher_text_hiding_en = snp_cipher_text_hiding;
+	init_args.snp_max_snp_asid = snp_max_snp_asid;
 	sev_platform_init(&init_args);
 }
 

Signature · 1 line

2.34.1

Quoted 8 lines · Ashish Kalra

From: Ashish Kalra <[email protected]>

Ciphertext hiding prevents host accesses from reading the ciphertext of SNP guest private memory. Instead of reading ciphertext, the host reads will see constant default values (0xff).

Ciphertext hiding separates the ASID space into SNP guest ASIDs and host ASIDs.

Uh, no. The only "host" ASID is '0'.

Quoted 3 lines

All SNP active guests must have an ASID less than or equal to MAX_SNP_ASID provided to the SNP_INIT_EX command. All SEV-legacy guests (SEV and SEV-ES) must be greater than MAX_SNP_ASID.

This is misleading, arguably wrong. The ASID space is already split into legacy+SEV and SEV-ES+. CTH further splits the SEV-ES+ space into SEV-ES and SEV-SNP+.

Quoted 1 line

Quoted 1 line

This patch-set adds two new module parameters to the KVM module, first

No "This patch".

Quoted 3 lines

to enable CipherTextHiding support and a user configurable MAX_SNP_ASID to define the system-wide maximum SNP ASID value. If this value is not set, then the ASID space is equally divided between SEV-SNP and SEV-ES guests.

This quite, and I suspect completely useless for every production use case. I also *really* dislike max_snp_asid. More below.

Quoted 10 lines

Signed-off-by Ashish Kalra <[email protected]>

---
 arch/x86/kvm/svm/sev.c | 50 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

arch/x86/kvm/svm/sev.c +0 -0

index 7a156ba07d1f..a905f755312a 100644

arch/x86/kvm/svm/sev.c static bool sev_es_debug_swap_enabled = true; · line 67

Quoted 10 lines

arch/x86/kvm/svm/sev.c +7 -0

@@ -58,6 +58,14 @@ static bool sev_es_debug_swap_enabled = true;
 module_param_named(debug_swap, sev_es_debug_swap_enabled, bool, 0444);
 static u64 sev_supported_vmsa_features;
 
+static bool cipher_text_hiding;
+module_param(cipher_text_hiding, bool, 0444);
+MODULE_PARM_DESC(cipher_text_hiding, "  if true, the PSP will enable Cipher Text Hiding");
+
+static int max_snp_asid;
+module_param(max_snp_asid, int, 0444);
+MODULE_PARM_DESC(max_snp_asid, "  override MAX_SNP_ASID for Cipher Text Hiding");

I'd much, much prefer proper document in Documentation/admin-guide/kernel-parameters.txt. The basic gist of the params is self-explanatory, but how all of this works is not.

And max_snp_asid is extremely misleading. Pretty much any reader is going to expect it to do what it says: set the max SNP ASID. But unless cipher_text_hiding is enabled, which it's not by default, the param does absolutely nothing.

To address both problems, can we somehow figure out a way to use a single param? The hardest part is probably coming up with a name. E.g.

  static int ciphertext_hiding_nr_asids;
  module_param(ciphertext_hiding_nr_asids, int, 0444);

Then a non-zero value means "enable CipherTexthiding", and effects the ASID carve-out. If we wanted to support the 50/50 split, we would use '-1' as an "auto" flag, i.e. enable CipherTexthiding and split the SEV-ES+ ASIDs.

Though to be honest,
I'd prefer to avoid that unless it's actually useful.

Ha! And I'm doubling down on that suggestion, because this code is wrong:

	if (boot_cpu_has(X86_FEATURE_SEV_ES)) {
		if (snp_max_snp_asid >= (min_sev_asid - 1))
			sev_es_supported = false;

		pr_info("SEV-ES %s (ASIDs %u - %u)\n",
			str_enabled_disabled(sev_es_supported),
			min_sev_asid > 1 ? snp_max_snp_asid ? snp_max_snp_asid + 1 : 1 :
							      0, min_sev_asid - 1);
	}

A non-zero snp_max_snp_asid shouldn't break SEV-ES if CipherTextHiding isn't supported.

Quoted 23 lines

arch/x86/kvm/svm/sev.c +3 -1

 #define AP_RESET_HOLD_NONE		0
 #define AP_RESET_HOLD_NAE_EVENT		1
 #define AP_RESET_HOLD_MSR_PROTO		2

@@ -85,6 +93,8 @@ static DEFINE_MUTEX(sev_bitmap_lock);
 unsigned int max_sev_asid;
 static unsigned int min_sev_asid;
 static unsigned long sev_me_mask;
+static unsigned int snp_max_snp_asid;
+static bool snp_cipher_text_hiding;
 static unsigned int nr_asids;
 static unsigned long *sev_asid_bitmap;
 static unsigned long *sev_reclaim_asid_bitmap;

@@ -171,7 +181,7 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
 	misc_cg_uncharge(type, sev->misc_cg, 1);
 }
 
-static int sev_asid_new(struct kvm_sev_info *sev)
+static int sev_asid_new(struct kvm_sev_info *sev, unsigned long vm_type)
 {
 	/*
 	 * SEV-enabled guests must use asid from min_sev_asid to max_sev_asid.

arch/x86/kvm/svm/sev.c static int sev_asid_new(struct kvm_sev_info *sev) · line 214

Quoted 6 lines

arch/x86/kvm/svm/sev.c +3 -0

@@ -199,6 +209,18 @@ static int sev_asid_new(struct kvm_sev_info *sev)
 
 	mutex_lock(&sev_bitmap_lock);
 
+	/*
+	 * When CipherTextHiding is enabled, all SNP guests must have an
+	 * ASID less than or equal to MAX_SNP_ASID provided on the

Wrap at ~80, not

arch/x86/kvm/svm/sev.c static int sev_asid_new(struct kvm_sev_info *sev) · line 216

Quoted 2 lines

arch/x86/kvm/svm/sev.c +2 -0

+	 * SNP_INIT_EX command and all the SEV-ES guests must have
+	 * an ASID greater than MAX_SNP_ASID.

Please don't referense MAX_SNP_ASID. The reader doesn't need to know what the PSP calls its parameter. What matters is the concept, and to a lesser extent KVM's param.

arch/x86/kvm/svm/sev.c static int sev_asid_new(struct kvm_sev_info *sev) · line 223

Quoted 7 lines

arch/x86/kvm/svm/sev.c +7 -0

+	 */
+	if (snp_cipher_text_hiding && sev->es_active) {
+		if (vm_type == KVM_X86_SNP_VM)
+			max_asid = snp_max_snp_asid;
+		else
+			min_asid = snp_max_snp_asid + 1;
+	}

Irrespective of the module params, I would much prefer to have a max_snp_asid param that is kept up-to-date regardless of whether or not CipherTextHiding is enabled.

Then you don't need a comment here, only a big fat comment in the code that configures the min/max ASIDs, which is going to be a gnarly comment no matter what we do. Oh, and this should be done before the

	if (min_asid > max_asid)
		return -ENOTTY;

sanity check.

And then drop the mix of ternary operators and if statements, and just do:

	unsigned int min_asid, max_asid, asid;
	bool retry = true;
	int ret;

	if (vm_type == KVM_X86_SNP_VM) {
		min_asid = min_snp_asid;
		max_asid = max_snp_asid;
	} else if (sev->es_active) {
		min_asid = min_sev_es_asid;
		max_asid = max_sev_es_asid;
	} else {
		min_asid = min_sev_asid;

		max_asid = max_sev_asid;
	}

	/*
	 * The min ASID can end up larger than the max if basic SEV support is
	 * effectively disabled by disallowing use of ASIDs for SEV guests.
	 * Ditto for SEV-ES guests when CipherTextHiding is enabled.
	 */

	if (min_asid > max_asid)
		return -ENOTTY;

Quoted 16 lines

arch/x86/kvm/svm/sev.c +6 -2

@@ -3040,14 +3074,18 @@ void __init sev_hardware_setup(void)
 								       "unusable" :
 								       "disabled",
 			min_sev_asid, max_sev_asid);
-	if (boot_cpu_has(X86_FEATURE_SEV_ES))
+	if (boot_cpu_has(X86_FEATURE_SEV_ES)) {
+		if (snp_max_snp_asid >= (min_sev_asid - 1))
+			sev_es_supported = false;
 		pr_info("SEV-ES %s (ASIDs %u - %u)\n",
 			str_enabled_disabled(sev_es_supported),
-			min_sev_asid > 1 ? 1 : 0, min_sev_asid - 1);
+			min_sev_asid > 1 ? snp_max_snp_asid ? snp_max_snp_asid + 1 : 1 :
+							      0, min_sev_asid - 1);
+	}
 	if (boot_cpu_has(X86_FEATURE_SEV_SNP))
 		pr_info("SEV-SNP %s (ASIDs %u - %u)\n",

arch/x86/kvm/svm/sev.c void __init sev_hardware_setup(void) · line 3088

Quoted 3 lines

arch/x86/kvm/svm/sev.c +1 -1

 			str_enabled_disabled(sev_snp_supported),
-			min_sev_asid > 1 ? 1 : 0, min_sev_asid - 1);
+			min_sev_asid > 1 ? 1 : 0, snp_max_snp_asid ? : min_sev_asid - 1);

Mixing in snp_max_snp_asid pretty much makes this is unreadable. Please rework this code to generate {min,max}_{sev,sev_es,snp,}_asid (add prep patches if necessary). I don't care terribly if ternary operators are used, but please don't chain them.

Quoted 15 lines

arch/x86/kvm/svm/sev.c +2 -0

 	sev_enabled = sev_supported;
 	sev_es_enabled = sev_es_supported;

@@ -3068,6 +3106,8 @@ void __init sev_hardware_setup(void)
 	 * Do both SNP and SEV initialization at KVM module load.
 	 */
 	init_args.probe = true;
+	init_args.cipher_text_hiding_en = snp_cipher_text_hiding;
+	init_args.snp_max_snp_asid = snp_max_snp_asid;
 	sev_platform_init(&init_args);
 }
 

Signature · 1 line

2.34.1

Quoted 4 lines · Sean Christopherson

	if (boot_cpu_has(X86_FEATURE_SEV_ES)) {
		if (snp_max_snp_asid >= (min_sev_asid - 1))
			sev_es_supported = false;

SEV-ES is disabled if SNP is using all ASIDs upto min_sev_asid - 1.

Quoted 6 lines

		pr_info("SEV-ES %s (ASIDs %u - %u)\n",
			str_enabled_disabled(sev_es_supported),
			min_sev_asid > 1 ? snp_max_snp_asid ? snp_max_snp_asid + 1 : 1 :
							      0, min_sev_asid - 1);
	}

Quoted 1 line

A non-zero snp_max_snp_asid shouldn't break SEV-ES if CipherTextHiding isn't supported.

I don't see above where SEV-ES is broken if snp_max_snp_asid is non-zero and CTH is enabled ?

Quoted 11 lines

arch/x86/kvm/svm/sev.c static int sev_asid_new(struct kvm_sev_info *sev) · line 223

Quoted 7 lines

arch/x86/kvm/svm/sev.c +7 -0

+	 */
+	if (snp_cipher_text_hiding && sev->es_active) {
+		if (vm_type == KVM_X86_SNP_VM)
+			max_asid = snp_max_snp_asid;
+		else
+			min_asid = snp_max_snp_asid + 1;
+	}

Irrespective of the module params, I would much prefer to have a max_snp_asid param that is kept up-to-date regardless of whether or not CipherTextHiding is enabled.

param ?