diff mbox series

[v2,4/4] iommu/amd: Enable Host SNP support after enabling IOMMU SNP support

Message ID afc1fb55dfcb1bccd8ee6730282b78a7e2f77a46.1738274758.git.ashish.kalra@amd.com (mailing list archive)
State New
Headers show
Series Fix broken SNP support with KVM module built-in | expand

Commit Message

Kalra, Ashish Jan. 31, 2025, 1:11 a.m. UTC 
From: Sean Christopherson <seanjc@google.com>

This patch fixes the current SNP host enabling code and effectively SNP
which is broken with respect to the KVM module being built-in.

SNP check on IOMMU is done during IOMMU PCI init (IOMMU_PCI_INIT stage).
And for that reason snp_rmptable_init() is currently invoked via
device_initcall() and cannot be invoked via subsys_initcall() as core
IOMMU subsystem gets initialized via subsys_initcall().

Essentially SNP host enabling code should be invoked before KVM
initialization, which is currently not the case when KVM is built-in
as SNP host support is enabled via device_initcall() which is
required as SNP check on IOMMU is done during IOMMU PCI init.

Hence, call snp_rmptable_init() early and directly from
iommu_snp_enable() (after checking and enabling IOMMU SNP support)
which enables SNP host support before KVM initialization with
kvm_amd module built-in.

Add additional handling for `iommu=off` or `amd_iommu=off` options.

If IOMMU initialization fails and iommu_snp_enable() is never reached,
CC_ATTR_HOST_SEV_SNP will be left set but that will cause PSP driver's
SNP_INIT to fail as IOMMU SNP sanity checks in SNP firmware will fail
as below:

[    9.723114] ccp 0000:23:00.1: sev enabled
[    9.727602] ccp 0000:23:00.1: psp enabled
[    9.732527] ccp 0000:a2:00.1: enabling device (0000 -> 0002)
[    9.739098] ccp 0000:a2:00.1: no command queues available
[    9.745167] ccp 0000:a2:00.1: psp enabled
[    9.805337] ccp 0000:23:00.1: SEV-SNP: failed to INIT rc -5, error 0x3
[    9.866426] ccp 0000:23:00.1: SEV API:1.53 build:5
...
and that will cause CC_ATTR_HOST_SEV_SNP flag to be cleared.

Fixes: 04d65a9dbb33 ("iommu/amd: Don't rely on external callers to enable IOMMU SNP support")
Co-developed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
 drivers/iommu/amd/init.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

Comments

Sean Christopherson Jan. 31, 2025, 1:48 a.m. UTC | #1 
On Fri, Jan 31, 2025, Ashish Kalra wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> This patch fixes the current SNP host enabling code and effectively SNP
  ^^^^^^^^^^
> ---
>  drivers/iommu/amd/init.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index c5cd92edada0..ee887aa4442f 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -3194,7 +3194,7 @@ static bool __init detect_ivrs(void)
>  	return true;
>  }
>  
> -static void iommu_snp_enable(void)
> +static __init void iommu_snp_enable(void)

If you're feeling nitpicky, adding "__init" could be done in a separate patch.

>  {
>  #ifdef CONFIG_KVM_AMD_SEV
>  	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> @@ -3219,6 +3219,11 @@ static void iommu_snp_enable(void)
>  		goto disable_snp;
>  	}
>  
> +	if (snp_rmptable_init()) {
> +		pr_warn("SNP: RMP initialization failed, SNP cannot be supported.\n");
> +		goto disable_snp;
> +	}
> +
>  	pr_info("IOMMU SNP support enabled.\n");
>  	return;
>  
> @@ -3426,18 +3431,23 @@ void __init amd_iommu_detect(void)
>  	int ret;
>  
>  	if (no_iommu || (iommu_detected && !gart_iommu_aperture))
> -		return;
> +		goto disable_snp;
>  
>  	if (!amd_iommu_sme_check())
> -		return;
> +		goto disable_snp;
>  
>  	ret = iommu_go_to_state(IOMMU_IVRS_DETECTED);
>  	if (ret)
> -		return;
> +		goto disable_snp;

This handles initial failure, but it won't handle the case where amd_iommu_prepare()
fails, as the iommu_go_to_state() call from amd_iommu_enable() will get
short-circuited.  I don't see any pleasant options.  Maybe this?

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index c5cd92edada0..436e47f13f8f 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3318,6 +3318,8 @@ static int __init iommu_go_to_state(enum iommu_init_state state)
                ret = state_next();
        }
 
+       if (ret && !amd_iommu_snp_en && cc_platform_has(CC_ATTR_HOST_SEV_SNP))
+               cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
        return ret;
 }
 

Somewhat of a side topic, what happens if the RMP is fully configured and _then_
IOMMU initialization fails?  I.e. if amd_iommu_init_pci() or amd_iommu_enable_interrupts()
fails?  Is that even survivable?

>  
>  	amd_iommu_detected = true;
>  	iommu_detected = 1;
>  	x86_init.iommu.iommu_init = amd_iommu_init;
> +	return;
> +
> +disable_snp:
> +	if (cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> +		cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
>  }
>  
>  /****************************************************************************
> -- 
> 2.34.1
>
diff mbox series

Patch

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index c5cd92edada0..ee887aa4442f 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3194,7 +3194,7 @@  static bool __init detect_ivrs(void)
 	return true;
 }
 
-static void iommu_snp_enable(void)
+static __init void iommu_snp_enable(void)
 {
 #ifdef CONFIG_KVM_AMD_SEV
 	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
@@ -3219,6 +3219,11 @@  static void iommu_snp_enable(void)
 		goto disable_snp;
 	}
 
+	if (snp_rmptable_init()) {
+		pr_warn("SNP: RMP initialization failed, SNP cannot be supported.\n");
+		goto disable_snp;
+	}
+
 	pr_info("IOMMU SNP support enabled.\n");
 	return;
 
@@ -3426,18 +3431,23 @@  void __init amd_iommu_detect(void)
 	int ret;
 
 	if (no_iommu || (iommu_detected && !gart_iommu_aperture))
-		return;
+		goto disable_snp;
 
 	if (!amd_iommu_sme_check())
-		return;
+		goto disable_snp;
 
 	ret = iommu_go_to_state(IOMMU_IVRS_DETECTED);
 	if (ret)
-		return;
+		goto disable_snp;
 
 	amd_iommu_detected = true;
 	iommu_detected = 1;
 	x86_init.iommu.iommu_init = amd_iommu_init;
+	return;
+
+disable_snp:
+	if (cc_platform_has(CC_ATTR_HOST_SEV_SNP))
+		cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
 }
 
 /****************************************************************************