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Commit d3e58022 authored by Robin Murphy's avatar Robin Murphy Committed by Greg Kroah-Hartman
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iommu/arm-smmu: Avoid constant zero in TLBI writes 



commit 4e4abae311e4b44aaf61f18a826fd7136037f199 upstream.

Apparently, some Qualcomm arm64 platforms which appear to expose their
SMMU global register space are still, in fact, using a hypervisor to
mediate it by trapping and emulating register accesses. Sadly, some
deployed versions of said trapping code have bugs wherein they go
horribly wrong for stores using r31 (i.e. XZR/WZR) as the source
register.

While this can be mitigated for GCC today by tweaking the constraints
for the implementation of writel_relaxed(), to avoid any potential
arms race with future compilers more aggressively optimising register
allocation, the simple way is to just remove all the problematic
constant zeros. For the write-only TLB operations, the actual value is
irrelevant anyway and any old nearby variable will provide a suitable
GPR to encode. The one point at which we really do need a zero to clear
a context bank happens before any of the TLB maintenance where crashes
have been reported, so is apparently not a problem... :/

Reported-by: default avatarAngeloGioacchino Del Regno <kholk11@gmail.com>
Tested-by: default avatarMarc Gonzalez <marc.w.gonzalez@free.fr>
Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Signed-off-by: default avatarMarc Gonzalez <marc.w.gonzalez@free.fr>
Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 31e216cf

drivers/iommu/arm-smmu.c

+12 −3
Original line number Diff line number Diff line
@@ -56,6 +56,15 @@ 
#include "io-pgtable.h"

#include "arm-smmu-regs.h"



/*

 * Apparently, some Qualcomm arm64 platforms which appear to expose their SMMU

 * global register space are still, in fact, using a hypervisor to mediate it

 * by trapping and emulating register accesses. Sadly, some deployed versions

 * of said trapping code have bugs wherein they go horribly wrong for stores

 * using r31 (i.e. XZR/WZR) as the source register.

 */

#define QCOM_DUMMY_VAL -1



#define ARM_MMU500_ACTLR_CPRE		(1 << 1)



#define ARM_MMU500_ACR_CACHE_LOCK	(1 << 26)
@@ -398,7 +407,7 @@ static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu, 
{

	unsigned int spin_cnt, delay;



	writel_relaxed(0, sync);

	writel_relaxed(QCOM_DUMMY_VAL, 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))
@@ -1637,8 +1646,8 @@ 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(QCOM_DUMMY_VAL, gr0_base + ARM_SMMU_GR0_TLBIALLH);

	writel_relaxed(QCOM_DUMMY_VAL, gr0_base + ARM_SMMU_GR0_TLBIALLNSNH);



	reg = readl_relaxed(ARM_SMMU_GR0_NS(smmu) + ARM_SMMU_GR0_sCR0);