Re: [PATCH v10 06/50] x86/sev: Add the host SEV-SNP initialization support

[Borislav Petkov]

On Tue, Nov 07, 2023 at 04:33:41PM -0600, Kalra, Ashish wrote:
> We will still need some method to tell the IOMMU driver if SNP
> support/feature is disabled by this function, for example, when CPU family
> and model is not supported by SNP and we jump to no_snp label.

See below.

> The reliable way for this to work is to ensure snp_rmptable_init() is called
> before IOMMU initialization and then IOMMU initialization depends on SNP
> feature flag setup by snp_rmptable_init() to enable SNP support on IOMMU or
> not.

Yes, this whole SNP initialization needs to be reworked and split this
way:

- early detection work which needs to be done once goes to
  bsp_init_amd(): that's basically your early_detect_mem_encrypt() stuff
  which needs to happen exactly only once and early.

- Any work like:

	 c->x86_phys_bits -= (cpuid_ebx(0x8000001f) >> 6) & 0x3f;

  and the like which needs to happen on each AP, gets put in a function
  which gets called by init_amd().

By the time IOMMU gets to init, you already know whether it should
enable SNP and check X86_FEATURE_SEV_SNP.

Finally, you call __snp_rmptable_init() which does the *per-CPU* init
work which is still pending.

Ok?

Ontop of the previous ontop patch:

---
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 6cc2074fcea3..a9c95e5d6b06 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -674,8 +674,19 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
 		if (!(msr & MSR_K7_HWCR_SMMLOCK))
 			goto clear_sev;
 
-		if (cpu_has(c, X86_FEATURE_SEV_SNP) && !early_rmptable_check())
-			goto clear_snp;
+		if (cpu_has(c, X86_FEATURE_SEV_SNP)) {
+			/*
+			 * RMP table entry format is not architectural and it can vary by processor
+			 * and is defined by the per-processor PPR. Restrict SNP support on the known
+			 * CPU model and family for which the RMP table entry format is currently
+			 * defined for.
+			 */
+			if (c->x86 != 0x19 || c->x86_model > 0xaf)
+				goto clear_snp;
+
+			if (!early_rmptable_check())
+				goto clear_snp;
+		}
 
 		return;
 
diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
index 9237c327ad6d..5a71df9ae4cb 100644
--- a/arch/x86/virt/svm/sev.c
+++ b/arch/x86/virt/svm/sev.c
@@ -199,14 +199,6 @@ static int __init snp_rmptable_init(void)
 	if (!amd_iommu_snp_en)
 		return 0;
 
-	/*
-	 * RMP table entry format is not architectural and it can vary by processor and
-	 * is defined by the per-processor PPR. Restrict SNP support on the known CPU
-	 * model and family for which the RMP table entry format is currently defined for.
-	 */
-	if (boot_cpu_data.x86 != 0x19 || boot_cpu_data.x86_model > 0xaf)
-		goto nosnp;
-
 	if (__snp_rmptable_init())
 		goto nosnp;
 
-- 
Regards/Gruss,
    Boris.

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