linux-kernel - [RFC PATCH v1 5/6] iommu/amd: Don't fail snp

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Message-Id: <20230123165128.28185-6-jpiotrowski@linux.microsoft.com>
Date:   Mon, 23 Jan 2023 16:51:27 +0000
From:   Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
To:     linux-kernel@...r.kernel.org
Cc:     Jeremi Piotrowski <jpiotrowski@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        linux-hyperv@...r.kernel.org,
        Brijesh Singh <brijesh.singh@....com>,
        Michael Roth <michael.roth@....com>,
        Ashish Kalra <ashish.kalra@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        iommu@...ts.linux.dev,
        Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
Subject: [RFC PATCH v1 5/6] iommu/amd: Don't fail snp_enable when running virtualized

From: Jeremi Piotrowski <jpiotrowski@...rosoft.com>

Hyper-V VMs do not have access to an IOMMU but can support hosting SNP
VMs. amd_iommu_snp_enable() is on the SNP init path and should not fail
in that case.

Signed-off-by: Jeremi Piotrowski <jpiotrowski@...ux.microsoft.com>
---
 drivers/iommu/amd/init.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index d1270e3c5baf..8049dbe78a27 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -3619,6 +3619,12 @@ int amd_iommu_pc_set_reg(struct amd_iommu *iommu, u8 bank, u8 cntr, u8 fxn, u64
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 int amd_iommu_snp_enable(void)
 {
+	/*
+	 * If we're running virtualized there doesn't have to be an IOMMU for SNP to work.
+	 */
+	if (init_state == IOMMU_NOT_FOUND && boot_cpu_has(X86_FEATURE_HYPERVISOR))
+		return 0;
+
 	/*
 	 * The SNP support requires that IOMMU must be enabled, and is
 	 * not configured in the passthrough mode.
-- 
2.25.1