iommu/arm-smmu-v3: Share process page tables

With Shared Virtual Addressing (SVA), we need to mirror CPU TTBR, TCR,
MAIR and ASIDs in SMMU contexts. Each SMMU has a single ASID space split
into two sets, shared and private. Shared ASIDs correspond to those
obtained from the arch ASID allocator, and private ASIDs are used for
"classic" map/unmap DMA.

A possible conflict happens when trying to use a shared ASID that has
already been allocated for private use by the SMMU driver. This will be
addressed in a later patch by replacing the private ASID. At the
moment we return -EBUSY.

Each mm_struct shared with the SMMU will have a single context
descriptor. Add a refcount to keep track of this. It will be protected
by the global SVA lock.

Introduce a new arm-smmu-v3-sva.c file and the CONFIG_ARM_SMMU_V3_SVA
option to let users opt in SVA support.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20200918101852.582559-9-jean-philippe@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>

drivers/iommu/Kconfig

@@ -308,6 +308,16 @@ config ARM_SMMU_V3
 	  Say Y here if your system includes an IOMMU device implementing
 	  the ARM SMMUv3 architecture.
 
+config ARM_SMMU_V3_SVA
+	bool "Shared Virtual Addressing support for the ARM SMMUv3"
+	depends on ARM_SMMU_V3
+	help
+	  Support for sharing process address spaces with devices using the
+	  SMMUv3.
+
+	  Say Y here if your system supports SVA extensions such as PCIe PASID
+	  and PRI.
+
 config S390_IOMMU
 	def_bool y if S390 && PCI
 	depends on S390 && PCI

drivers/iommu/arm/arm-smmu-v3/Makefile

@@ -1,2 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o
+obj-$(CONFIG_ARM_SMMU_V3) += arm_smmu_v3.o
+arm_smmu_v3-objs-y += arm-smmu-v3.o
+arm_smmu_v3-objs-$(CONFIG_ARM_SMMU_V3_SVA) += arm-smmu-v3-sva.o
+arm_smmu_v3-objs := $(arm_smmu_v3-objs-y)

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c

@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Implementation of the IOMMU SVA API for the ARM SMMUv3
+ */
+
+#include <linux/mm.h>
+#include <linux/mmu_context.h>
+#include <linux/slab.h>
+
+#include "arm-smmu-v3.h"
+#include "../../io-pgtable-arm.h"
+
+static struct arm_smmu_ctx_desc *
+arm_smmu_share_asid(struct mm_struct *mm, u16 asid)
+{
+	struct arm_smmu_ctx_desc *cd;
+
+	cd = xa_load(&arm_smmu_asid_xa, asid);
+	if (!cd)
+		return NULL;
+
+	if (cd->mm) {
+		if (WARN_ON(cd->mm != mm))
+			return ERR_PTR(-EINVAL);
+		/* All devices bound to this mm use the same cd struct. */
+		refcount_inc(&cd->refs);
+		return cd;
+	}
+
+	/* Ouch, ASID is already in use for a private cd. */
+	return ERR_PTR(-EBUSY);
+}
+
+__maybe_unused
+static struct arm_smmu_ctx_desc *arm_smmu_alloc_shared_cd(struct mm_struct *mm)
+{
+	u16 asid;
+	int err = 0;
+	u64 tcr, par, reg;
+	struct arm_smmu_ctx_desc *cd;
+	struct arm_smmu_ctx_desc *ret = NULL;
+
+	asid = arm64_mm_context_get(mm);
+	if (!asid)
+		return ERR_PTR(-ESRCH);
+
+	cd = kzalloc(sizeof(*cd), GFP_KERNEL);
+	if (!cd) {
+		err = -ENOMEM;
+		goto out_put_context;
+	}
+
+	refcount_set(&cd->refs, 1);
+
+	mutex_lock(&arm_smmu_asid_lock);
+	ret = arm_smmu_share_asid(mm, asid);
+	if (ret) {
+		mutex_unlock(&arm_smmu_asid_lock);
+		goto out_free_cd;
+	}
+
+	err = xa_insert(&arm_smmu_asid_xa, asid, cd, GFP_KERNEL);
+	mutex_unlock(&arm_smmu_asid_lock);
+
+	if (err)
+		goto out_free_asid;
+
+	tcr = FIELD_PREP(CTXDESC_CD_0_TCR_T0SZ, 64ULL - vabits_actual) |
+	      FIELD_PREP(CTXDESC_CD_0_TCR_IRGN0, ARM_LPAE_TCR_RGN_WBWA) |
+	      FIELD_PREP(CTXDESC_CD_0_TCR_ORGN0, ARM_LPAE_TCR_RGN_WBWA) |
+	      FIELD_PREP(CTXDESC_CD_0_TCR_SH0, ARM_LPAE_TCR_SH_IS) |
+	      CTXDESC_CD_0_TCR_EPD1 | CTXDESC_CD_0_AA64;
+
+	switch (PAGE_SIZE) {
+	case SZ_4K:
+		tcr |= FIELD_PREP(CTXDESC_CD_0_TCR_TG0, ARM_LPAE_TCR_TG0_4K);
+		break;
+	case SZ_16K:
+		tcr |= FIELD_PREP(CTXDESC_CD_0_TCR_TG0, ARM_LPAE_TCR_TG0_16K);
+		break;
+	case SZ_64K:
+		tcr |= FIELD_PREP(CTXDESC_CD_0_TCR_TG0, ARM_LPAE_TCR_TG0_64K);
+		break;
+	default:
+		WARN_ON(1);
+		err = -EINVAL;
+		goto out_free_asid;
+	}
+
+	reg = read_sanitised_ftr_reg(SYS_ID_AA64MMFR0_EL1);
+	par = cpuid_feature_extract_unsigned_field(reg, ID_AA64MMFR0_PARANGE_SHIFT);
+	tcr |= FIELD_PREP(CTXDESC_CD_0_TCR_IPS, par);
+
+	cd->ttbr = virt_to_phys(mm->pgd);
+	cd->tcr = tcr;
+	/*
+	 * MAIR value is pretty much constant and global, so we can just get it
+	 * from the current CPU register
+	 */
+	cd->mair = read_sysreg(mair_el1);
+	cd->asid = asid;
+	cd->mm = mm;
+
+	return cd;
+
+out_free_asid:
+	arm_smmu_free_asid(cd);
+out_free_cd:
+	kfree(cd);
+out_put_context:
+	arm64_mm_context_put(mm);
+	return err < 0 ? ERR_PTR(err) : ret;
+}
+
+__maybe_unused
+static void arm_smmu_free_shared_cd(struct arm_smmu_ctx_desc *cd)
+{
+	if (arm_smmu_free_asid(cd)) {
+		/* Unpin ASID */
+		arm64_mm_context_put(cd->mm);
+		kfree(cd);
+	}
+}

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -73,7 +73,8 @@ struct arm_smmu_option_prop {
 	const char *prop;
 };
 
-static DEFINE_XARRAY_ALLOC1(asid_xa);
+DEFINE_XARRAY_ALLOC1(arm_smmu_asid_xa);
+DEFINE_MUTEX(arm_smmu_asid_lock);
 
 static struct arm_smmu_option_prop arm_smmu_options[] = {
 	{ ARM_SMMU_OPT_SKIP_PREFETCH, "hisilicon,broken-prefetch-cmd" },
@@ -1013,7 +1014,8 @@ static int arm_smmu_write_ctx_desc(struct arm_smmu_domain *smmu_domain,
 #ifdef __BIG_ENDIAN
 			CTXDESC_CD_0_ENDI |
 #endif
-			CTXDESC_CD_0_R | CTXDESC_CD_0_A | CTXDESC_CD_0_ASET |
+			CTXDESC_CD_0_R | CTXDESC_CD_0_A |
+			(cd->mm ? 0 : CTXDESC_CD_0_ASET) |
 			CTXDESC_CD_0_AA64 |
 			FIELD_PREP(CTXDESC_CD_0_ASID, cd->asid) |
 			CTXDESC_CD_0_V;
@@ -1117,12 +1119,20 @@ static void arm_smmu_free_cd_tables(struct arm_smmu_domain *smmu_domain)
 	cdcfg->cdtab = NULL;
 }
 
-static void arm_smmu_free_asid(struct arm_smmu_ctx_desc *cd)
+bool arm_smmu_free_asid(struct arm_smmu_ctx_desc *cd)
 {
-	if (!cd->asid)
-		return;
+	bool free;
+	struct arm_smmu_ctx_desc *old_cd;
 
-	xa_erase(&asid_xa, cd->asid);
+	if (!cd->asid)
+		return false;
+
+	free = refcount_dec_and_test(&cd->refs);
+	if (free) {
+		old_cd = xa_erase(&arm_smmu_asid_xa, cd->asid);
+		WARN_ON(old_cd != cd);
+	}
+	return free;
 }
 
 /* Stream table manipulation functions */
@@ -1810,9 +1820,12 @@ static void arm_smmu_domain_free(struct iommu_domain *domain)
 	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1) {
 		struct arm_smmu_s1_cfg *cfg = &smmu_domain->s1_cfg;
 
+		/* Prevent SVA from touching the CD while we're freeing it */
+		mutex_lock(&arm_smmu_asid_lock);
 		if (cfg->cdcfg.cdtab)
 			arm_smmu_free_cd_tables(smmu_domain);
 		arm_smmu_free_asid(&cfg->cd);
+		mutex_unlock(&arm_smmu_asid_lock);
 	} else {
 		struct arm_smmu_s2_cfg *cfg = &smmu_domain->s2_cfg;
 		if (cfg->vmid)
@@ -1832,10 +1845,14 @@ static int arm_smmu_domain_finalise_s1(struct arm_smmu_domain *smmu_domain,
 	struct arm_smmu_s1_cfg *cfg = &smmu_domain->s1_cfg;
 	typeof(&pgtbl_cfg->arm_lpae_s1_cfg.tcr) tcr = &pgtbl_cfg->arm_lpae_s1_cfg.tcr;
 
-	ret = xa_alloc(&asid_xa, &asid, &cfg->cd,
+	refcount_set(&cfg->cd.refs, 1);
+
+	/* Prevent SVA from modifying the ASID until it is written to the CD */
+	mutex_lock(&arm_smmu_asid_lock);
+	ret = xa_alloc(&arm_smmu_asid_xa, &asid, &cfg->cd,
 		       XA_LIMIT(1, (1 << smmu->asid_bits) - 1), GFP_KERNEL);
 	if (ret)
-		return ret;
+		goto out_unlock;
 
 	cfg->s1cdmax = master->ssid_bits;
 
@@ -1863,12 +1880,15 @@ static int arm_smmu_domain_finalise_s1(struct arm_smmu_domain *smmu_domain,
 	if (ret)
 		goto out_free_cd_tables;
 
+	mutex_unlock(&arm_smmu_asid_lock);
 	return 0;
 
 out_free_cd_tables:
 	arm_smmu_free_cd_tables(smmu_domain);
 out_free_asid:
 	arm_smmu_free_asid(&cfg->cd);
+out_unlock:
+	mutex_unlock(&arm_smmu_asid_lock);
 	return ret;
 }
 

drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h

@@ -540,6 +540,9 @@ struct arm_smmu_ctx_desc {
 	u64				ttbr;
 	u64				tcr;
 	u64				mair;
+
+	refcount_t			refs;
+	struct mm_struct		*mm;
 };
 
 struct arm_smmu_l1_ctx_desc {
@@ -673,4 +676,9 @@ struct arm_smmu_domain {
 	spinlock_t			devices_lock;
 };
 
+extern struct xarray arm_smmu_asid_xa;
+extern struct mutex arm_smmu_asid_lock;
+
+bool arm_smmu_free_asid(struct arm_smmu_ctx_desc *cd);
+
 #endif /* _ARM_SMMU_V3_H */