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From:   Nadav Amit <nadav.amit@gmail.com>
To:     Joerg Roedel <joro@8bytes.org>
Cc:     Nadav Amit <namit@vmware.com>, Will Deacon <will@kernel.org>,
        Jiajun Cao <caojiajun@vmware.com>,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 4/4] iommu/amd: Do not use flush-queue when NpCache is on
Date:   Mon, 24 May 2021 15:41:59 -0700
Message-Id: <20210524224159.32807-5-namit@vmware.com>
In-Reply-To: <20210524224159.32807-1-namit@vmware.com>
References: <20210524224159.32807-1-namit@vmware.com>
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From: Nadav Amit <namit@vmware.com>

Do not use flush-queue on virtualized environments, where the NpCache
capability of the IOMMU is set. This is required to reduce
virtualization overheads.

This change follows a similar change to Intel's VT-d and a detailed
explanation as for the rationale is described in commit 29b32839725f
("iommu/vt-d: Do not use flush-queue when caching-mode is on").

Cc: Joerg Roedel <joro@8bytes.org>
Cc: Will Deacon <will@kernel.org>
Cc: Jiajun Cao <caojiajun@vmware.com>
Cc: iommu@lists.linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Nadav Amit <namit@vmware.com>
---
 drivers/iommu/amd/init.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index d006724f4dc2..ba3b76ed776d 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -1850,8 +1850,13 @@ static int __init iommu_init_pci(struct amd_iommu *iommu)
 	if (ret)
 		return ret;
 
-	if (iommu->cap & (1UL << IOMMU_CAP_NPCACHE))
+	if (iommu->cap & (1UL << IOMMU_CAP_NPCACHE)) {
+		if (!amd_iommu_unmap_flush)
+			pr_warn_once("IOMMU batching is disabled due to virtualization");
+
 		amd_iommu_np_cache = true;
+		amd_iommu_unmap_flush = true;
+	}
 
 	init_iommu_perf_ctr(iommu);
 
-- 
2.25.1