[Xen-devel] [PATCH v2] arm, smmu: backport "Disable stalling faults for all endpoints"

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

From: Stefano Stabellini <stefanos@xxxxxxxxxx>

Backport commit 3714ce1d6655098ee69ede632883e5874d67e4ab
"iommu/arm-smmu: Disable stalling faults for all endpoints" from the
Linux kernel. This works-around Erratum #842869.

Original commit message:

  Enabling stalling faults can result in hardware deadlock on poorly
  designed systems, particularly those with a PCI root complex upstream of
  the SMMU.

  Although it's not really Linux's job to save hardware integrators from
  their own misfortune, it *is* our job to stop userspace (e.g. VFIO
  clients) from hosing the system for everybody else, even if they might
  already be required to have elevated privileges.

  Given that the fault handling code currently executes entirely in IRQ
  context, there is nothing that can sensibly be done to recover from
  things like page faults anyway, so let's rip this code out for now and
  avoid the potential for deadlock.

  Cc: <stable@xxxxxxxxxxxxxxx>
  Fixes: 48ec83bcbcf5 ("iommu/arm-smmu: Add initial driver support for ARM 
SMMUv3 devices")
  Reported-by: Matt Evans <matt.evans@xxxxxxx>
  Signed-off-by: Will Deacon <will.deacon@xxxxxxx>

Signed-off-by: Stefano Stabellini <stefanos@xxxxxxxxxx>

---
Changes in v2:
- add Erratum to docs/misc/arm/silicon-errata.txt
- add in-code comment about Erratum
---
 docs/misc/arm/silicon-errata.txt   |  1 +
 xen/drivers/passthrough/arm/smmu.c | 40 ++++++++++++--------------------------
 2 files changed, 13 insertions(+), 28 deletions(-)

diff --git a/docs/misc/arm/silicon-errata.txt b/docs/misc/arm/silicon-errata.txt
index c9854c3..906bf5f 100644
--- a/docs/misc/arm/silicon-errata.txt
+++ b/docs/misc/arm/silicon-errata.txt
@@ -48,3 +48,4 @@ stable hypervisors.
 | ARM            | Cortex-A57      | #852523         | N/A                     
|
 | ARM            | Cortex-A57      | #832075         | ARM64_ERRATUM_832075    
|
 | ARM            | Cortex-A57      | #834220         | ARM64_ERRATUM_834220    
|
+| ARM            | MMU-500         | #842869         | N/A                     
|
diff --git a/xen/drivers/passthrough/arm/smmu.c 
b/xen/drivers/passthrough/arm/smmu.c
index b510399..9612c0f 100644
--- a/xen/drivers/passthrough/arm/smmu.c
+++ b/xen/drivers/passthrough/arm/smmu.c
@@ -898,8 +898,7 @@ static void arm_smmu_tlb_inv_context(struct arm_smmu_domain 
*smmu_domain)
 
 static irqreturn_t arm_smmu_context_fault(int irq, void *dev)
 {
-       int flags, ret;
-       u32 fsr, far, fsynr, resume;
+       u32 fsr, far, fsynr;
        unsigned long iova;
        struct iommu_domain *domain = dev;
        struct arm_smmu_domain *smmu_domain = domain->priv;
@@ -913,13 +912,7 @@ static irqreturn_t arm_smmu_context_fault(int irq, void 
*dev)
        if (!(fsr & FSR_FAULT))
                return IRQ_NONE;
 
-       if (fsr & FSR_IGN)
-               dev_err_ratelimited(smmu->dev,
-                                   "Unexpected context fault (fsr 0x%x)\n",
-                                   fsr);
-
        fsynr = readl_relaxed(cb_base + ARM_SMMU_CB_FSYNR0);
-       flags = fsynr & FSYNR0_WNR ? IOMMU_FAULT_WRITE : IOMMU_FAULT_READ;
 
        far = readl_relaxed(cb_base + ARM_SMMU_CB_FAR_LO);
        iova = far;
@@ -928,25 +921,12 @@ static irqreturn_t arm_smmu_context_fault(int irq, void 
*dev)
        iova |= ((unsigned long)far << 32);
 #endif
 
-       if (!report_iommu_fault(domain, smmu->dev, iova, flags)) {
-               ret = IRQ_HANDLED;
-               resume = RESUME_RETRY;
-       } else {
-               dev_err_ratelimited(smmu->dev,
-                   "Unhandled context fault: iova=0x%08lx, fsynr=0x%x, 
cb=%d\n",
-                   iova, fsynr, cfg->cbndx);
-               ret = IRQ_NONE;
-               resume = RESUME_TERMINATE;
-       }
-
-       /* Clear the faulting FSR */
+       dev_err_ratelimited(smmu->dev,
+       "Unhandled context fault: fsr=0x%x, iova=0x%08lx, fsynr=0x%x, cb=%d\n",
+                           fsr, iova, fsynr, cfg->cbndx);
+ 
        writel(fsr, cb_base + ARM_SMMU_CB_FSR);
-
-       /* Retry or terminate any stalled transactions */
-       if (fsr & FSR_SS)
-               writel_relaxed(resume, cb_base + ARM_SMMU_CB_RESUME);
-
-       return ret;
+       return IRQ_HANDLED;
 }
 
 static irqreturn_t arm_smmu_global_fault(int irq, void *dev)
@@ -1180,8 +1160,12 @@ static void arm_smmu_init_context_bank(struct 
arm_smmu_domain *smmu_domain)
                writel_relaxed(reg, cb_base + ARM_SMMU_CB_S1_MAIR0);
        }
 
-       /* SCTLR */
-       reg = SCTLR_CFCFG | SCTLR_CFIE | SCTLR_CFRE | SCTLR_M | SCTLR_EAE_SBOP;
+       /*
+        * SCTLR
+        *
+        * Do not set SCTLR_CFCFG, because of Erratum #842869
+        */
+       reg = SCTLR_CFIE | SCTLR_CFRE | SCTLR_M | SCTLR_EAE_SBOP;
        if (stage1)
                reg |= SCTLR_S1_ASIDPNE;
 #ifdef __BIG_ENDIAN
-- 
1.9.1


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