linux-kernel - Re: [PATCH] Revert "iommu/io-pgtable-arm: Optimise non-coherent unmap"

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Message-ID: <20240905155330.GA15246@willie-the-truck>
Date: Thu, 5 Sep 2024 16:53:30 +0100
From: Will Deacon <will@...nel.org>
To: Rob Clark <robdclark@...il.com>
Cc: iommu@...ts.linux.dev, linux-arm-msm@...r.kernel.org,
	freedreno@...ts.freedesktop.org, Ashish Mhetre <amhetre@...dia.com>,
	Rob Clark <robdclark@...omium.org>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "iommu/io-pgtable-arm: Optimise non-coherent
 unmap"

Hi Rob,

On Thu, Sep 05, 2024 at 05:49:56AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> This reverts commit 85b715a334583488ad7fbd3001fe6fd617b7d4c0.
> 
> It was causing gpu smmu faults on x1e80100.
> 
> I _think_ what is causing this is the change in ordering of
> __arm_lpae_clear_pte() (dma_sync_single_for_device() on the pgtable
> memory) and io_pgtable_tlb_flush_walk().  I'm not entirely sure how
> this patch is supposed to work correctly in the face of other
> concurrent translations (to buffers unrelated to the one being
> unmapped(), because after the io_pgtable_tlb_flush_walk() we can have
> stale data read back into the tlb.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/iommu/io-pgtable-arm.c | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)

Please can you try the diff below, instead?

Will

--->8

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index 0e67f1721a3d..0a32e9499e2c 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -672,7 +672,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
                /* Clear the remaining entries */
                __arm_lpae_clear_pte(ptep, &iop->cfg, i);
 
-               if (gather && !iommu_iotlb_gather_queued(gather))
+               if (!iommu_iotlb_gather_queued(gather))
                        for (int j = 0; j < i; j++)
                                io_pgtable_tlb_add_page(iop, gather, iova + j * size, size);