Re: [PATCH v3 2/5] iommu/arm-smmu: Add support for split pagetables

Will Deacon
2020-01-09T14:33:41Z

On Mon, Dec 16, 2019 at 09:37:48AM -0700, Jordan Crouse wrote:
> Add support to enable split pagetables (TTBR1) if the supporting driver
> requests it via the DOMAIN_ATTR_SPLIT_TABLES flag. When enabled, the driver
> will set up the TTBR0 and TTBR1 regions and program the default domain
> pagetable on TTBR1.
>
> After attaching the device, the value of he domain attribute can
> be queried to see if the split pagetables were successfully programmed.
> Furthermore the domain geometry will be updated so that the caller can
> determine the active region for the pagetable that was programmed.
>
> Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
> ---
>
> drivers/iommu/arm-smmu.c | 40 +++++++++++++++++++++++++++++++++++-----
> drivers/iommu/arm-smmu.h | 45 +++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 74 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index c106406..7b59116 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -538,9 +538,17 @@ static void arm_smmu_init_context_bank(struct arm_smmu_domain *smmu_domain,
> cb->ttbr[0] = pgtbl_cfg->arm_v7s_cfg.ttbr;
> cb->ttbr[1] = 0;
> } else {
> - cb->ttbr[0] = pgtbl_cfg->arm_lpae_s1_cfg.ttbr;
> - cb->ttbr[0] |= FIELD_PREP(TTBRn_ASID, cfg->asid);
> - cb->ttbr[1] = FIELD_PREP(TTBRn_ASID, cfg->asid);
> + if (pgtbl_cfg->quirks & IO_PGTABLE_QUIRK_ARM_TTBR1) {
> + cb->ttbr[0] = FIELD_PREP(TTBRn_ASID, cfg->asid);
> + cb->ttbr[1] = pgtbl_cfg->arm_lpae_s1_cfg.ttbr;
> + cb->ttbr[1] |=
> + FIELD_PREP(TTBRn_ASID, cfg->asid);
> + } else {
> + cb->ttbr[0] = pgtbl_cfg->arm_lpae_s1_cfg.ttbr;
> + cb->ttbr[0] |=
> + FIELD_PREP(TTBRn_ASID, cfg->asid);
> + cb->ttbr[1] = FIELD_PREP(TTBRn_ASID, cfg->asid);
> + }

I still don't understand why you have to set the ASID in both of the TTBRs.
Assuming TCR.A1 is clear, then we should only need to set the field in
TTBR0.

> }
> } else {
> cb->ttbr[0] = pgtbl_cfg->arm_lpae_s2_cfg.vttbr;
> @@ -651,6 +659,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> enum io_pgtable_fmt fmt;
> struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
> struct arm_smmu_cfg *cfg = &smmu_domain->cfg;
> + u32 quirks = 0;
>
> mutex_lock(&smmu_domain->init_mutex);
> if (smmu_domain->smmu)
> @@ -719,6 +728,8 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> oas = smmu->ipa_size;
> if (cfg->fmt == ARM_SMMU_CTX_FMT_AARCH64) {
> fmt = ARM_64_LPAE_S1;
> + if (smmu_domain->split_pagetables)
> + quirks |= IO_PGTABLE_QUIRK_ARM_TTBR1;
> } else if (cfg->fmt == ARM_SMMU_CTX_FMT_AARCH32_L) {
> fmt = ARM_32_LPAE_S1;
> ias = min(ias, 32UL);
> @@ -788,6 +799,7 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
> .coherent_walk = smmu->features & ARM_SMMU_FEAT_COHERENT_WALK,
> .tlb = smmu_domain->flush_ops,
> .iommu_dev = smmu->dev,
> + .quirks = quirks,
> };
>
> if (smmu_domain->non_strict)
> @@ -801,8 +813,15 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain,
>
> /* Update the domain's page sizes to reflect the page table format */
> domain->pgsize_bitmap = pgtbl_cfg.pgsize_bitmap;
> - domain->geometry.aperture_end = (1UL << ias) - 1;
> - domain->geometry.force_aperture = true;
> +
> + if (pgtbl_cfg.quirks & IO_PGTABLE_QUIRK_ARM_TTBR1) {
> + domain->geometry.aperture_start = ~((1ULL << ias) - 1);
> + domain->geometry.aperture_end = ~0UL;
> + } else {
> + domain->geometry.aperture_end = (1UL << ias) - 1;
> + domain->geometry.force_aperture = true;
> + smmu_domain->split_pagetables = false;
> + }
>
> /* Initialise the context bank with our page table cfg */
> arm_smmu_init_context_bank(smmu_domain, &pgtbl_cfg);
> @@ -1484,6 +1503,9 @@ static int arm_smmu_domain_get_attr(struct iommu_domain *domain,
> case DOMAIN_ATTR_NESTING:
> *(int *)data = (smmu_domain->stage == ARM_SMMU_DOMAIN_NESTED);
> return 0;
> + case DOMAIN_ATTR_SPLIT_TABLES:
> + *(int *)data = smmu_domain->split_pagetables;
> + return 0;
> default:
> return -ENODEV;
> }
> @@ -1524,6 +1546,14 @@ static int arm_smmu_domain_set_attr(struct iommu_domain *domain,
> else
> smmu_domain->stage = ARM_SMMU_DOMAIN_S1;
> break;
> + case DOMAIN_ATTR_SPLIT_TABLES:
> + if (smmu_domain->smmu) {
> + ret = -EPERM;
> + goto out_unlock;
> + }
> + if (*(int *)data)
> + smmu_domain->split_pagetables = true;
> + break;
> default:
> ret = -ENODEV;
> }
> diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> index afab9de..68526cc 100644
> --- a/drivers/iommu/arm-smmu.h
> +++ b/drivers/iommu/arm-smmu.h
> @@ -177,6 +177,16 @@ enum arm_smmu_cbar_type {
> #define TCR_IRGN0 GENMASK(9, 8)
> #define TCR_T0SZ GENMASK(5, 0)
>
> +#define TCR_TG1 GENMASK(31, 30)
> +
> +#define TG0_4K 0
> +#define TG0_64K 1
> +#define TG0_16K 2
> +
> +#define TG1_16K 1
> +#define TG1_4K 2
> +#define TG1_64K 3
> +
> #define ARM_SMMU_CB_CONTEXTIDR 0x34
> #define ARM_SMMU_CB_S1_MAIR0 0x38
> #define ARM_SMMU_CB_S1_MAIR1 0x3c
> @@ -329,16 +339,39 @@ struct arm_smmu_domain {
> struct mutex init_mutex; /* Protects smmu pointer */
> spinlock_t cb_lock; /* Serialises ATS1* ops and TLB syncs */
> struct iommu_domain domain;
> + bool split_pagetables;
> };
>
> +static inline u32 arm_smmu_lpae_tcr_tg(struct io_pgtable_cfg *cfg)
> +{
> + u32 val;
> +
> + if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_TTBR1))
> + return FIELD_PREP(TCR_TG0, cfg->arm_lpae_s1_cfg.tcr.tg);
> +
> + val = FIELD_PREP(TCR_TG1, cfg->arm_lpae_s1_cfg.tcr.tg);
> +
> + if (cfg->arm_lpae_s1_cfg.tcr.tg == TG1_4K)
> + val |= FIELD_PREP(TCR_TG0, TG0_4K);
> + else if (cfg->arm_lpae_s1_cfg.tcr.tg == TG1_16K)
> + val |= FIELD_PREP(TCR_TG0, TG0_16K);
> + else
> + val |= FIELD_PREP(TCR_TG0, TG0_64K);

This looks like it's making assumptions about the order in which page-tables
are installed, which I'd really like to avoid. See below.

> static inline u32 arm_smmu_lpae_tcr(struct io_pgtable_cfg *cfg)
> {
> - return TCR_EPD1 |
> - FIELD_PREP(TCR_TG0, cfg->arm_lpae_s1_cfg.tcr.tg) |
> - FIELD_PREP(TCR_SH0, cfg->arm_lpae_s1_cfg.tcr.sh) |
> - FIELD_PREP(TCR_ORGN0, cfg->arm_lpae_s1_cfg.tcr.orgn) |
> - FIELD_PREP(TCR_IRGN0, cfg->arm_lpae_s1_cfg.tcr.irgn) |
> - FIELD_PREP(TCR_T0SZ, cfg->arm_lpae_s1_cfg.tcr.tsz);
> + u32 tcr = FIELD_PREP(TCR_SH0, cfg->arm_lpae_s1_cfg.tcr.sh) |
> + FIELD_PREP(TCR_ORGN0, cfg->arm_lpae_s1_cfg.tcr.orgn) |
> + FIELD_PREP(TCR_IRGN0, cfg->arm_lpae_s1_cfg.tcr.irgn) |
> + FIELD_PREP(TCR_T0SZ, cfg->arm_lpae_s1_cfg.tcr.tsz);
> +
> + if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_TTBR1))
> + return tcr | TCR_EPD1 | arm_smmu_lpae_tcr_tg(cfg);

This is interesting. If the intention is to have both TTBR0 and TTBR1
used concurrently by different domains, then we probably need to be a bit
smarter about setting TCR_EPDx. Can we do something like start off with them
both set, and then just clear the one we want when installing a page-table?

Will