Re: [PATCH v1 1/2] iommu/tegra-smmu: Defer attachment of display clients

Nicolin Chen
2021-04-08T09:44:43Z

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On Mon, Mar 29, 2021 at 02:32:55AM +0300, Dmitry Osipenko wrote:
> All consumer-grade Android and Chromebook devices show a splash screen
> on boot and then display is left enabled when kernel is booted. This
> behaviour is unacceptable in a case of implicit IOMMU domains to which
> devices are attached during kernel boot since devices, like display
> controller, may perform DMA at that time. We can work around this problem
> by deferring the enable of SMMU translation for a specific devices,
> like a display controller, until the first IOMMU mapping is created,
> which works good enough in practice because by that time h/w is already
> stopped.
>
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>

For both patches:
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Nicolin Chen <nicoleotsuka@gmail.com>

The WAR looks good to me. Perhaps Thierry would give some input.

Another topic:
I think this may help work around the mc-errors, which we have
been facing on Tegra210 also when we enable IOMMU_DOMAIN_DMA.
(attached a test patch rebasing on these two)

However, GPU would also report errors using DMA domain:

nouveau 57000000.gpu: acr: firmware unavailable
nouveau 57000000.gpu: pmu: firmware unavailable
nouveau 57000000.gpu: gr: firmware unavailable
tegra-mc 70019000.memory-controller: gpusrd: read @0x00000000fffbe200: Security violation (TrustZone violation)
nouveau 57000000.gpu: DRM: failed to create kernel channel, -22
tegra-mc 70019000.memory-controller: gpusrd: read @0x00000000fffad000: Security violation (TrustZone violation)
nouveau 57000000.gpu: fifo: SCHED_ERROR 20 []
nouveau 57000000.gpu: fifo: SCHED_ERROR 20 []

Looking at the address, seems that GPU allocated memory in 32-bit
physical address space behind SMMU, so a violation happened after
turning on DMA domain I guess...

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From 20b58a74fee0c7b961b92f9118ad69a12199e6a5 Mon Sep 17 00:00:00 2001
From: Nicolin Chen <nicolinc@nvidia.com>
Date: Thu, 12 Dec 2019 17:46:50 -0800
Subject: [PATCH 6/7] iommu/tegra-smmu: Add IOMMU_DOMAIN_DMA

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
drivers/iommu/tegra-smmu.c | 39 ++++++++++++++++++++++----------------
1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 8104f001e679..eff10d1ec568 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -15,6 +15,7 @@
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/dma-mapping.h>
+#include <linux/dma-iommu.h>

#include <soc/tegra/ahb.h>
#include <soc/tegra/mc.h>
@@ -297,35 +298,29 @@ static struct iommu_domain *tegra_smmu_domain_alloc(unsigned type)
{
struct tegra_smmu_as *as;

- if (type != IOMMU_DOMAIN_UNMANAGED)
+ if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
return NULL;

as = kzalloc(sizeof(*as), GFP_KERNEL);
if (!as)
return NULL;

+ if (type == IOMMU_DOMAIN_DMA && iommu_get_dma_cookie(&as->domain))
+ goto free_as;
+
as->attr = SMMU_PD_READABLE | SMMU_PD_WRITABLE | SMMU_PD_NONSECURE;

as->pd = alloc_page(GFP_KERNEL | __GFP_DMA | __GFP_ZERO);
- if (!as->pd) {
- kfree(as);
- return NULL;
- }
+ if (!as->pd)
+ goto put_dma_cookie;

as->count = kcalloc(SMMU_NUM_PDE, sizeof(u32), GFP_KERNEL);
- if (!as->count) {
- __free_page(as->pd);
- kfree(as);
- return NULL;
- }
+ if (!as->count)
+ goto free_pd_range;

as->pts = kcalloc(SMMU_NUM_PDE, sizeof(*as->pts), GFP_KERNEL);
- if (!as->pts) {
- kfree(as->count);
- __free_page(as->pd);
- kfree(as);
- return NULL;
- }
+ if (!as->pts)
+ goto free_pts;

spin_lock_init(&as->lock);

@@ -335,6 +330,17 @@ static struct iommu_domain *tegra_smmu_domain_alloc(unsigned type)
as->attached_devices_need_sync = true;

return &as->domain;
+
+free_pts:
+ kfree(as->pts);
+free_pd_range:
+ __free_page(as->pd);
+put_dma_cookie:
+ iommu_put_dma_cookie(&as->domain);
+free_as:
+ kfree(as);
+
+ return NULL;
}

static void tegra_smmu_domain_free(struct iommu_domain *domain)
@@ -346,6 +352,7 @@ static void tegra_smmu_domain_free(struct iommu_domain *domain)
WARN_ON_ONCE(as->use_count);
kfree(as->count);
kfree(as->pts);
+ iommu_put_dma_cookie(domain);
kfree(as);
}

--
2.17.1

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