linux-kernel - Re: [PATCH v1 03/26] iommu/amd: Don't rely on external callers to enable IOMMU SNP support

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Date: Thu, 4 Jan 2024 11:30:47 +0100
From: Borislav Petkov <bp@...en8.de>
To: Michael Roth <michael.roth@....com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-coco@...ts.linux.dev,
	linux-mm@...ck.org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
	ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
	vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
	dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
	peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
	rientjes@...gle.com, tobin@....com, vbabka@...e.cz,
	kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
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	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com,
	pankaj.gupta@....com, liam.merwick@...cle.com, zhi.a.wang@...el.com
Subject: Re: [PATCH v1 03/26] iommu/amd: Don't rely on external callers to
 enable IOMMU SNP support

On Sat, Dec 30, 2023 at 10:19:31AM -0600, Michael Roth wrote:
> +static void iommu_snp_enable(void)
> +{
> +#ifdef CONFIG_KVM_AMD_SEV
> +	if (!cpu_feature_enabled(X86_FEATURE_SEV_SNP))
> +		return;
> +	/*
> +	 * The SNP support requires that IOMMU must be enabled, and is
> +	 * not configured in the passthrough mode.
> +	 */
> +	if (no_iommu || iommu_default_passthrough()) {
> +		pr_err("SNP: IOMMU is disabled or configured in passthrough mode, SNP cannot be supported.\n");
> +		return;
> +	}
> +
> +	amd_iommu_snp_en = check_feature(FEATURE_SNP);
> +	if (!amd_iommu_snp_en) {
> +		pr_err("SNP: IOMMU SNP feature is not enabled, SNP cannot be supported.\n");
> +		return;
> +	}
> +
> +	pr_info("IOMMU SNP support is enabled.\n");
> +
> +	/* Enforce IOMMU v1 pagetable when SNP is enabled. */
> +	if (amd_iommu_pgtable != AMD_IOMMU_V1) {
> +		pr_warn("Forcing use of AMD IOMMU v1 page table due to SNP.\n");
> +		amd_iommu_pgtable = AMD_IOMMU_V1;
> +	}

Kernel code usually says simple "<bla> enabled" not "<bla> is enabled".
Other than that, LGTM.

---

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 1ed2ef22a0fb..2f1517acaba0 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3231,17 +3231,17 @@ static void iommu_snp_enable(void)
 	 * not configured in the passthrough mode.
 	 */
 	if (no_iommu || iommu_default_passthrough()) {
-		pr_err("SNP: IOMMU is disabled or configured in passthrough mode, SNP cannot be supported.\n");
+		pr_err("SNP: IOMMU disabled or configured in passthrough mode, SNP cannot be supported.\n");
 		return;
 	}
 
 	amd_iommu_snp_en = check_feature(FEATURE_SNP);
 	if (!amd_iommu_snp_en) {
-		pr_err("SNP: IOMMU SNP feature is not enabled, SNP cannot be supported.\n");
+		pr_err("SNP: IOMMU SNP feature not enabled, SNP cannot be supported.\n");
 		return;
 	}
 
-	pr_info("IOMMU SNP support is enabled.\n");
+	pr_info("IOMMU SNP support enabled.\n");
 
 	/* Enforce IOMMU v1 pagetable when SNP is enabled. */
 	if (amd_iommu_pgtable != AMD_IOMMU_V1) {


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette