linux-kernel - [PATCH 1/1] iommu/amd: Preserve default DTE fields when updating Host Page Table Root

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Message-Id: <20250106191413.3107140-1-alejandro.j.jimenez@oracle.com>
Date: Mon,  6 Jan 2025 19:14:13 +0000
From: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
To: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Cc: joro@...tes.org, suravee.suthikulpanit@....com, vasant.hegde@....com,
        will@...nel.org, jgg@...dia.com, joao.m.martins@...cle.com,
        boris.ostrovsky@...cle.com, alejandro.j.jimenez@...cle.com
Subject: [PATCH 1/1] iommu/amd: Preserve default DTE fields when updating Host Page Table Root

When updating the page table root field on the DTE, avoid overwriting any
bits that are already set. The earlier call to make_clear_dte() writes
default values that all DTEs must have set (currently DTE[V]), and those
must be preserved.

Currently this doesn't cause problems since the page table root update is
the first field that is set after make_clear_dte() is called, and
DTE_FLAG_V is set again later along with the permission bits (IR/IW).
Remove this redundant assignment too.

Fixes: fd5dff9de4be ("iommu/amd: Modify set_dte_entry() to use 256-bit DTE helpers")
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@...cle.com>
---
 drivers/iommu/amd/iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 20177e18eb0d..a8c17b602c95 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -2052,12 +2052,12 @@ static void set_dte_entry(struct amd_iommu *iommu,
 	make_clear_dte(dev_data, dte, &new);
 
 	if (domain->iop.mode != PAGE_MODE_NONE)
-		new.data[0] = iommu_virt_to_phys(domain->iop.root);
+		new.data[0] |= iommu_virt_to_phys(domain->iop.root);
 
 	new.data[0] |= (domain->iop.mode & DEV_ENTRY_MODE_MASK)
 		    << DEV_ENTRY_MODE_SHIFT;
 
-	new.data[0] |= DTE_FLAG_IR | DTE_FLAG_IW | DTE_FLAG_V;
+	new.data[0] |= DTE_FLAG_IR | DTE_FLAG_IW;
 
 	/*
 	 * When SNP is enabled, we can only support TV=1 with non-zero domain ID.

base-commit: 1f37ef785d54b27e304c189038697a845259408a
-- 
2.39.3