linux-kernel - [RFC PATCH 1/5] iommu/virtio-iommu: Correct the values of granule and nr

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Message-Id: <20231106071226.9656-2-tina.zhang@intel.com>
Date:   Mon,  6 Nov 2023 02:12:22 -0500
From:   Tina Zhang <tina.zhang@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>, joro@...tes.org,
        will@...nel.org, Yi Liu <yi.l.liu@...el.com>
Cc:     virtualization@...ts.linux-foundation.org, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Tina Zhang <tina.zhang@...el.com>
Subject: [RFC PATCH 1/5] iommu/virtio-iommu: Correct the values of granule and nr_pages

The value of granule is ilog2(pgsize). When the value of pgsize isn't
a power of two, granule would make pgsize less than the actual size of
pgsize. E.g., if pgsize = 0x6000 and granule = ilog2(gather->pgsize), then
granule = 0xe. 2^0xe = 0x4000 makes the pgsize (0x4000) smaller than the
actual pgsize (0x6000). Invalidating IOTLB with smaller range would lead
to cache incoherence. So, roundup pgsize value to the nearest power of 2
to make sure the granule won't make pgsize less than the actual size. The
value of "gather->end - gather->start + 1" also needs similar adjustment.

Signed-off-by: Tina Zhang <tina.zhang@...el.com>
---
 drivers/iommu/virtio-iommu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 08e310672e57..b1ceaac974e2 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -1289,8 +1289,8 @@ static void viommu_iotlb_sync(struct iommu_domain *domain,
 		if (!gather->pgsize)
 			return;
 
-		granule = ilog2(gather->pgsize);
-		nr_pages = (gather->end - gather->start + 1) >> granule;
+		granule = ilog2(__roundup_pow_of_two(gather->pgsize));
+		nr_pages = __roundup_pow_of_two(gather->end - gather->start + 1) >> granule;
 		req = (struct virtio_iommu_req_invalidate) {
 			.head.type	= VIRTIO_IOMMU_T_INVALIDATE,
 			.inv_gran	= cpu_to_le16(VIRTIO_IOMMU_INVAL_G_VA),
-- 
2.39.3