[PATCH v8 07/12] iommu/arm-smmu-v3: Share process page tables

[Jean-Philippe Brucker <jean-philippe@linaro.org>]

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.

Acked-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
---
 drivers/iommu/arm-smmu-v3.c | 150 +++++++++++++++++++++++++++++++++++-
 1 file changed, 146 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 937aa1af428d5..cabd942e4cbf3 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -22,6 +22,7 @@
 #include <linux/iommu.h>
 #include <linux/iopoll.h>
 #include <linux/module.h>
+#include <linux/mmu_context.h>
 #include <linux/msi.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
@@ -33,6 +34,8 @@
 
 #include <linux/amba/bus.h>
 
+#include "io-pgtable-arm.h"
+
 /* MMIO registers */
 #define ARM_SMMU_IDR0			0x0
 #define IDR0_ST_LVL			GENMASK(28, 27)
@@ -589,6 +592,9 @@ struct arm_smmu_ctx_desc {
 	u64				ttbr;
 	u64				tcr;
 	u64				mair;
+
+	refcount_t			refs;
+	struct mm_struct		*mm;
 };
 
 struct arm_smmu_l1_ctx_desc {
@@ -727,6 +733,7 @@ struct arm_smmu_option_prop {
 };
 
 static DEFINE_XARRAY_ALLOC1(asid_xa);
+static DEFINE_MUTEX(sva_lock);
 
 static struct arm_smmu_option_prop arm_smmu_options[] = {
 	{ ARM_SMMU_OPT_SKIP_PREFETCH, "hisilicon,broken-prefetch-cmd" },
@@ -1662,7 +1669,8 @@ 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;
@@ -1766,12 +1774,144 @@ 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)
+static void arm_smmu_init_cd(struct arm_smmu_ctx_desc *cd)
 {
+	refcount_set(&cd->refs, 1);
+}
+
+static bool arm_smmu_free_asid(struct arm_smmu_ctx_desc *cd)
+{
+	bool free;
+	struct arm_smmu_ctx_desc *old_cd;
+
 	if (!cd->asid)
-		return;
+		return false;
+
+	free = refcount_dec_and_test(&cd->refs);
+	if (free) {
+		old_cd = xa_erase(&asid_xa, cd->asid);
+		WARN_ON(old_cd != cd);
+	}
+	return free;
+}
+
+static struct arm_smmu_ctx_desc *arm_smmu_share_asid(u16 asid)
+{
+	struct arm_smmu_ctx_desc *cd;
 
-	xa_erase(&asid_xa, cd->asid);
+	cd = xa_load(&asid_xa, asid);
+	if (!cd)
+		return NULL;
+
+	if (cd->mm) {
+		/* 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 ret = 0;
+	u64 tcr, par, reg;
+	struct arm_smmu_ctx_desc *cd;
+	struct arm_smmu_ctx_desc *old_cd = NULL;
+
+	lockdep_assert_held(&sva_lock);
+
+	asid = mm_context_get(mm);
+	if (!asid)
+		return ERR_PTR(-ESRCH);
+
+	cd = kzalloc(sizeof(*cd), GFP_KERNEL);
+	if (!cd) {
+		ret = -ENOMEM;
+		goto err_put_context;
+	}
+
+	arm_smmu_init_cd(cd);
+
+	old_cd = arm_smmu_share_asid(asid);
+	if (IS_ERR(old_cd)) {
+		ret = PTR_ERR(old_cd);
+		goto err_free_cd;
+	} else if (old_cd) {
+		if (WARN_ON(old_cd->mm != mm)) {
+			ret = -EINVAL;
+			goto err_free_cd;
+		}
+		kfree(cd);
+		mm_context_put(mm);
+		return old_cd;
+	}
+
+	/* Fails if a private ASID has been allocated since we last checked */
+	ret = xa_insert(&asid_xa, asid, cd, GFP_KERNEL);
+	if (ret)
+		goto err_free_cd;
+
+	tcr = FIELD_PREP(CTXDESC_CD_0_TCR_T0SZ, 64ULL - VA_BITS) |
+	      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);
+		ret = -EINVAL;
+		goto err_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;
+
+err_free_asid:
+	arm_smmu_free_asid(cd);
+err_free_cd:
+	kfree(cd);
+err_put_context:
+	mm_context_put(mm);
+	return ERR_PTR(ret);
+}
+
+__maybe_unused
+static void arm_smmu_free_shared_cd(struct arm_smmu_ctx_desc *cd)
+{
+	lockdep_assert_held(&sva_lock);
+
+	if (arm_smmu_free_asid(cd)) {
+		/* Unpin ASID */
+		mm_context_put(cd->mm);
+		kfree(cd);
+	}
 }
 
 /* Stream table manipulation functions */
@@ -2481,6 +2621,8 @@ 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;
 
+	arm_smmu_init_cd(&cfg->cd);
+
 	ret = xa_alloc(&asid_xa, &asid, &cfg->cd,
 		       XA_LIMIT(1, (1 << smmu->asid_bits) - 1), GFP_KERNEL);
 	if (ret)
-- 
2.27.0

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