Re: [PATCH v8 05/16] x86/sev: Cache the secrets page address

[Nikunj A. Dadhania]

On 4/16/2024 8:15 PM, Borislav Petkov wrote:
> On Thu, Feb 15, 2024 at 05:01:17PM +0530, Nikunj A Dadhania wrote:
>> +/* Secrets page physical address from the CC blob */
>> +static u64 secrets_pa __ro_after_init;
> 
> Since you're going to use this during runtime (are you?), 

Yes, this is used during runtime, during initial boot will be used by Secure TSC and later by sev-guest driver.

> why don't you put in here the result of:
> 
> 	ioremap_encrypted(secrets_pa, PAGE_SIZE);
> 
> so that you can have it ready and not even have to ioremap each time?

Yes, that is a good idea. If I map in sev.c, what is the right place to iounmap ? Is it safe to keep it mapped until reboot/shutdown ?

> And then you iounmap on driver teardown.
> 
>> +static void __init set_secrets_pa(const struct cc_blob_sev_info *cc_info)
>> +{
>> +	if (cc_info && cc_info->secrets_phys && cc_info->secrets_len == PAGE_SIZE)
>> +		secrets_pa = cc_info->secrets_phys;
>> +}
> 
> Why is this a separate function if it is called only once and it is
> a trivial function at that?

Sure, I will change it.

> 
> Also, can the driver continue without secrets page?

No.

> If not, then you need to unwind.
>
By unwind, do you mean unmapping in the driver?
 
>>  bool __init snp_init(struct boot_params *bp)
>>  {
>>  	struct cc_blob_sev_info *cc_info;
>> @@ -2099,6 +2079,8 @@ bool __init snp_init(struct boot_params *bp)
>>  	if (!cc_info)
>>  		return false;
>>  
>> +	set_secrets_pa(cc_info);
>> +
>>  	setup_cpuid_table(cc_info);
>>  
>>  	/*
>> @@ -2246,16 +2228,16 @@ static struct platform_device sev_guest_device = {
>>  static int __init snp_init_platform_device(void)
>>  {
>>  	struct sev_guest_platform_data data;
>> -	u64 gpa;
>>  
>>  	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
>>  		return -ENODEV;
>>  
>> -	gpa = get_secrets_page();
>> -	if (!gpa)
>> +	if (!secrets_pa) {
>> +		pr_err("SNP secrets page not found\n");
>>  		return -ENODEV;
>> +	}
> 
> Yeah, no, you need to error out in snp_init() and not drag it around to
> snp_init_platform_device().

snp_init() is called from sme_enable(), and does not handle failure from snp_init()

How about the below diff?

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index e9925df21010..5e052f972138 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -114,7 +114,7 @@ struct snp_req_data {
 };
 
 struct sev_guest_platform_data {
-	u64 secrets_gpa;
+	void *secrets_page;
 };
 
 /*
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 95003b809438..14c88e4f98ba 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -90,6 +90,9 @@ static struct ghcb *boot_ghcb __section(".data");
 /* Bitmap of SEV features supported by the hypervisor */
 static u64 sev_hv_features __ro_after_init;
 
+/* Secrets page address mapped from the CC blob physical address */
+static void *secrets_page __ro_after_init;
+
 /* #VC handler runtime per-CPU data */
 struct sev_es_runtime_data {
 	struct ghcb ghcb_page;
@@ -616,54 +619,16 @@ void noinstr __sev_es_nmi_complete(void)
 	__sev_put_ghcb(&state);
 }
 
-static u64 __init get_secrets_page(void)
-{
-	u64 pa_data = boot_params.cc_blob_address;
-	struct cc_blob_sev_info info;
-	void *map;
-
-	/*
-	 * The CC blob contains the address of the secrets page, check if the
-	 * blob is present.
-	 */
-	if (!pa_data)
-		return 0;
-
-	map = early_memremap(pa_data, sizeof(info));
-	if (!map) {
-		pr_err("Unable to locate SNP secrets page: failed to map the Confidential Computing blob.\n");
-		return 0;
-	}
-	memcpy(&info, map, sizeof(info));
-	early_memunmap(map, sizeof(info));
-
-	/* smoke-test the secrets page passed */
-	if (!info.secrets_phys || info.secrets_len != PAGE_SIZE)
-		return 0;
-
-	return info.secrets_phys;
-}
-
 static u64 __init get_snp_jump_table_addr(void)
 {
 	struct snp_secrets_page_layout *layout;
-	void __iomem *mem;
-	u64 pa, addr;
-
-	pa = get_secrets_page();
-	if (!pa)
-		return 0;
+	u64 addr;
 
-	mem = ioremap_encrypted(pa, PAGE_SIZE);
-	if (!mem) {
-		pr_err("Unable to locate AP jump table address: failed to map the SNP secrets page.\n");
+	if (!secrets_page)
 		return 0;
-	}
-
-	layout = (__force struct snp_secrets_page_layout *)mem;
 
+	layout = (__force struct snp_secrets_page_layout *)secrets_page;
 	addr = layout->os_area.ap_jump_table_pa;
-	iounmap(mem);
 
 	return addr;
 }
@@ -2118,6 +2083,14 @@ bool __init snp_init(struct boot_params *bp)
 	if (!cc_info)
 		return false;
 
+	if (cc_info->secrets_phys && cc_info->secrets_len == PAGE_SIZE) {
+		secrets_page = ioremap_encrypted(cc_info->secrets_phys, PAGE_SIZE);
+		if (!secrets_page) {
+			pr_err("Unable to map secrets page\n");
+			return false;
+		}
+	}
+
 	setup_cpuid_table(cc_info);
 
 	/*
@@ -2265,16 +2238,11 @@ static struct platform_device sev_guest_device = {
 static int __init snp_init_platform_device(void)
 {
 	struct sev_guest_platform_data data;
-	u64 gpa;
-
-	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
-		return -ENODEV;
 
-	gpa = get_secrets_page();
-	if (!gpa)
+	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP) || !secrets_page)
 		return -ENODEV;
 
-	data.secrets_gpa = gpa;
+	data.secrets_page = secrets_page;
 	if (platform_device_add_data(&sev_guest_device, &data, sizeof(data)))
 		return -ENODEV;
 
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index dbc04229f7ac..4cef4e108130 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -820,12 +820,10 @@ static void unregister_sev_tsm(void *data)
 
 static int __init sev_guest_probe(struct platform_device *pdev)
 {
-	struct snp_secrets_page_layout *layout;
 	struct sev_guest_platform_data *data;
 	struct device *dev = &pdev->dev;
 	struct snp_guest_dev *snp_dev;
 	struct miscdevice *misc;
-	void __iomem *mapping;
 	int ret;
 
 	if (!cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
@@ -835,28 +833,24 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 		return -ENODEV;
 
 	data = (struct sev_guest_platform_data *)dev->platform_data;
-	mapping = ioremap_encrypted(data->secrets_gpa, PAGE_SIZE);
-	if (!mapping)
+	if (!data->secrets_page)
 		return -ENODEV;
 
-	layout = (__force void *)mapping;
-
-	ret = -ENOMEM;
 	snp_dev = devm_kzalloc(&pdev->dev, sizeof(struct snp_guest_dev), GFP_KERNEL);
 	if (!snp_dev)
-		goto e_unmap;
+		return -ENOMEM;
 
 	ret = -EINVAL;
-	snp_dev->layout = layout;
+	snp_dev->layout = (__force struct snp_secrets_page_layout *)data->secrets_page;
 	if (!snp_assign_vmpck(snp_dev, vmpck_id)) {
 		dev_err(dev, "invalid vmpck id %u\n", vmpck_id);
-		goto e_unmap;
+		return ret;
 	}
 
 	/* Verify that VMPCK is not zero. */
 	if (snp_is_vmpck_empty(snp_dev)) {
 		dev_err(dev, "vmpck id %u is null\n", vmpck_id);
-		goto e_unmap;
+		return ret;
 	}
 
 	platform_set_drvdata(pdev, snp_dev);
@@ -865,7 +859,7 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	/* Allocate secret request and response message for double buffering */
 	snp_dev->secret_request = kzalloc(SNP_GUEST_MSG_SIZE, GFP_KERNEL);
 	if (!snp_dev->secret_request)
-		goto e_unmap;
+		return ret;
 
 	snp_dev->secret_response = kzalloc(SNP_GUEST_MSG_SIZE, GFP_KERNEL);
 	if (!snp_dev->secret_response)
@@ -925,8 +919,6 @@ static int __init sev_guest_probe(struct platform_device *pdev)
 	kfree(snp_dev->secret_response);
 e_free_secret_req:
 	kfree(snp_dev->secret_request);
-e_unmap:
-	iounmap(mapping);
 	return ret;
 }


Regards
Nikunj