linux-kernel - [PATCH 4/5] drm/msm: Use separate ASID for each set of pgtables

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Date:   Sun, 21 Aug 2022 11:19:05 -0700
From:   Rob Clark <robdclark@...il.com>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        Rob Clark <robdclark@...omium.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH 4/5] drm/msm: Use separate ASID for each set of pgtables

From: Rob Clark <robdclark@...omium.org>

Optimize TLB invalidation by using different ASID for each set of
pgtables.  There can be scenarios where multiple processes end up
with the same ASID (such as >256 processes using the GPU), but this
is harmless, it will only result in some over-invalidation (but
less over-invalidation compared to using ASID=0 for all processes)

Signed-off-by: Rob Clark <robdclark@...omium.org>
---
 drivers/gpu/drm/msm/msm_iommu.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
index a54ed354578b..94c8c09980d1 100644
--- a/drivers/gpu/drm/msm/msm_iommu.c
+++ b/drivers/gpu/drm/msm/msm_iommu.c
@@ -33,6 +33,8 @@ static int msm_iommu_pagetable_unmap(struct msm_mmu *mmu, u64 iova,
 		size_t size)
 {
 	struct msm_iommu_pagetable *pagetable = to_pagetable(mmu);
+	struct adreno_smmu_priv *adreno_smmu =
+		dev_get_drvdata(pagetable->parent->dev);
 	struct io_pgtable_ops *ops = pagetable->pgtbl_ops;
 	size_t unmapped = 0;
 
@@ -43,7 +45,7 @@ static int msm_iommu_pagetable_unmap(struct msm_mmu *mmu, u64 iova,
 		size -= 4096;
 	}
 
-	iommu_flush_iotlb_all(to_msm_iommu(pagetable->parent)->domain);
+	adreno_smmu->tlb_inv_by_id(adreno_smmu->cookie, pagetable->asid);
 
 	return (unmapped == size) ? 0 : -EINVAL;
 }
@@ -147,6 +149,7 @@ static int msm_fault_handler(struct iommu_domain *domain, struct device *dev,
 
 struct msm_mmu *msm_iommu_pagetable_create(struct msm_mmu *parent)
 {
+	static atomic_t asid = ATOMIC_INIT(1);
 	struct adreno_smmu_priv *adreno_smmu = dev_get_drvdata(parent->dev);
 	struct msm_iommu *iommu = to_msm_iommu(parent);
 	struct msm_iommu_pagetable *pagetable;
@@ -210,12 +213,14 @@ struct msm_mmu *msm_iommu_pagetable_create(struct msm_mmu *parent)
 	pagetable->ttbr = ttbr0_cfg.arm_lpae_s1_cfg.ttbr;
 
 	/*
-	 * TODO we would like each set of page tables to have a unique ASID
-	 * to optimize TLB invalidation.  But iommu_flush_iotlb_all() will
-	 * end up flushing the ASID used for TTBR1 pagetables, which is not
-	 * what we want.  So for now just use the same ASID as TTBR1.
+	 * ASID 0 is used for kernel mapped buffers in TTBR1, which we
+	 * do not need to invalidate when unmapping from TTBR0 pgtables.
+	 * The hw ASID is at *least* 8b, but can be 16b.  We just assume
+	 * the worst:
 	 */
 	pagetable->asid = 0;
+	while (!pagetable->asid)
+		pagetable->asid = atomic_inc_return(&asid) & 0xff;
 
 	return &pagetable->base;
 }
-- 
2.37.2