Messages in this thread Patch in this message | | | Subject | Re: [PATCH] arm64/io: Don't use WZR in writel | From | Robin Murphy <> | Date | Mon, 18 Mar 2019 16:04:03 +0000 |
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On 12/03/2019 12:36, Marc Gonzalez wrote: > On 24/02/2019 04:53, Bjorn Andersson wrote: > >> On Sat 23 Feb 10:37 PST 2019, Marc Zyngier wrote: >> >>> On Sat, 23 Feb 2019 18:12:54 +0000, Bjorn Andersson wrote: >>>> >>>> On Mon 11 Feb 06:59 PST 2019, Marc Zyngier wrote: >>>> >>>>> On 11/02/2019 14:29, AngeloGioacchino Del Regno wrote: >>>>> >>>>>> Also, just one more thing: yes this thing is going ARM64-wide and >>>>>> - from my findings - it's targeting certain Qualcomm SoCs, but... >>>>>> I'm not sure that only QC is affected by that, others may as well >>>>>> have the same stupid bug. >>>>> >>>>> At the moment, only QC SoCs seem to be affected, probably because >>>>> everyone else has debugged their hypervisor (or most likely doesn't >>>>> bother with shipping one). >>>>> >>>>> In all honesty, we need some information from QC here: which SoCs are >>>>> affected, what is the exact nature of the bug, can it be triggered from >>>>> EL0. Randomly papering over symptoms is not something I really like >>>>> doing, and is likely to generate problems on unaffected systems. >>>> >>>> The bug at hand is that the XZR is not deemed a valid source in the >>>> virtualization of the SMMU registers. It was identified and fixed for >>>> all platforms that are shipping kernels based on v4.9 or later. >>> >>> When you say "fixed": Do you mean fixed in the firmware? Or by adding >>> a workaround in the shipped kernel? >> >> I mean that it's fixed in the firmware. >> >>> If the former, is this part of an official QC statement, with an >>> associated erratum number? >> >> I don't know, will get back to you on this one. >> >>> Is this really limited to the SMMU accesses? >> >> Yes. >> >>>> As such Angelo's list of affected platforms covers the high-profile >>>> ones. In particular MSM8996 and MSM8998 is getting pretty good support >>>> upstream, if we can figure out a way around this issue. >>> >>> We'd need an exhaustive list of the affected SoCs, and work out if we >>> can limit the hack to the SMMU driver (cc'ing Robin, who's the one >>> who'd know about it). >> >> I will try to compose a list. > > FWIW, I have just been bitten by this issue. I needed to enable an SMMU to > filter PCIe EP accesses to system RAM (or something). I'm using an APQ8098 > MEDIABOX dev board. My system hangs in arm_smmu_device_reset() doing: > > /* Invalidate the TLB, just in case */ > writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLH); > writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH); > > > With the 'Z' constraint, gcc generates: > > str wzr, [x0] > > without the 'Z' constraint, gcc generates: > > mov w1, 0 > str w1, [x0] > > > I can work around the problem using the following patch: > > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c > index 045d93884164..93117519aed8 100644 > --- a/drivers/iommu/arm-smmu.c > +++ b/drivers/iommu/arm-smmu.c > @@ -59,6 +59,11 @@ > > #include "arm-smmu-regs.h" > > +static inline void qcom_writel(u32 val, volatile void __iomem *addr) > +{ > + asm volatile("str %w0, [%1]" : : "r" (val), "r" (addr)); > +} > + > #define ARM_MMU500_ACTLR_CPRE (1 << 1) > > #define ARM_MMU500_ACR_CACHE_LOCK (1 << 26) > @@ -422,7 +427,7 @@ static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu, > { > unsigned int spin_cnt, delay; > > - writel_relaxed(0, sync); > + qcom_writel(0, sync); > for (delay = 1; delay < TLB_LOOP_TIMEOUT; delay *= 2) { > for (spin_cnt = TLB_SPIN_COUNT; spin_cnt > 0; spin_cnt--) { > if (!(readl_relaxed(status) & sTLBGSTATUS_GSACTIVE)) > @@ -1760,8 +1765,8 @@ static void arm_smmu_device_reset(struct arm_smmu_device *smmu) > } > > /* Invalidate the TLB, just in case */ > - writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLH); > - writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH); > + qcom_writel(0, gr0_base + ARM_SMMU_GR0_TLBIALLH); > + qcom_writel(0, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH); > > reg = readl_relaxed(ARM_SMMU_GR0_NS(smmu) + ARM_SMMU_GR0_sCR0); > > > > > Can a quirk be used to work around the issue? > Or can we just "pessimize" the 3 writes for everybody? > (Might be cheaper than a test anyway)
If it really is just the SMMU driver which is affected, we can work around it for free (not counting the 'cost' of slightly-weird-looking code, of course). If the diff below works as expected, I'll write it up properly.
Robin. ----->8----- diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c index 045d93884164..7ff29e33298f 100644 --- a/drivers/iommu/arm-smmu.c +++ b/drivers/iommu/arm-smmu.c @@ -422,7 +422,7 @@ static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu, { unsigned int spin_cnt, delay;
- writel_relaxed(0, sync); + writel_relaxed((unsigned long)sync, sync); for (delay = 1; delay < TLB_LOOP_TIMEOUT; delay *= 2) { for (spin_cnt = TLB_SPIN_COUNT; spin_cnt > 0; spin_cnt--) { if (!(readl_relaxed(status) & sTLBGSTATUS_GSACTIVE)) @@ -681,7 +681,12 @@ static void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx)
/* Unassigned context banks only need disabling */ if (!cfg) { - writel_relaxed(0, cb_base + ARM_SMMU_CB_SCTLR); + /* + * For Qualcomm reasons, we want to guarantee that we write a + * zero from a register which is not WZR. Fortunately, the cfg + * logic here plays right into our hands... + */ + writel_relaxed((unsigned long)cfg, cb_base + ARM_SMMU_CB_SCTLR); return; }
@@ -1760,8 +1765,8 @@ static void arm_smmu_device_reset(struct arm_smmu_device *smmu) }
/* Invalidate the TLB, just in case */ - writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLH); - writel_relaxed(0, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH); + writel_relaxed(reg, gr0_base + ARM_SMMU_GR0_TLBIALLH); + writel_relaxed(reg, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH);
reg = readl_relaxed(ARM_SMMU_GR0_NS(smmu) + ARM_SMMU_GR0_sCR0);
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