Hi Jean,
On 12/18/19 5:07 PM, Jean-Philippe Brucker wrote:
> On Tue, Dec 17, 2019 at 05:43:59PM +0100, Auger Eric wrote:
>>> -static void arm_smmu_write_ctx_desc(struct arm_smmu_device *smmu,
>>> - struct arm_smmu_s1_cfg *cfg)
>>> +static int arm_smmu_write_ctx_desc(struct arm_smmu_domain *smmu_domain,
>>> + int ssid, struct arm_smmu_ctx_desc *cd)
>>> {
>>> - u64 val;
>>> - __le64 *cdptr = cfg->table.ptr;
>>> -
>>> /*
>>> - * We don't need to issue any invalidation here, as we'll invalidate
>>> - * the STE when installing the new entry anyway.
>>> + * This function handles the following cases:
>>> + *
>>> + * (1) Install primary CD, for normal DMA traffic (SSID = 0).
>>> + * (2) Install a secondary CD, for SID+SSID traffic.
>>> + * (3) Update ASID of a CD. Atomically write the first 64 bits of the
>>> + * CD, then invalidate the old entry and mappings.
>>> + * (4) Remove a secondary CD.
>> I see arm_smmu_write_ctx_desc getting called with non null cd in
>> arm_smmu_attach_dev but I do not see it removed in the detach path?
>
> No we don't have to remove the primary CD, since detach clears the STE and
> frees the CD tables.
OK
>
>>> */
>>> - val = arm_smmu_cpu_tcr_to_cd(cfg->cd.tcr) |
>>> -#ifdef __BIG_ENDIAN
>>> - CTXDESC_CD_0_ENDI |
>>> -#endif
>>> - CTXDESC_CD_0_R | CTXDESC_CD_0_A | CTXDESC_CD_0_ASET |
>>> - CTXDESC_CD_0_AA64 | FIELD_PREP(CTXDESC_CD_0_ASID, cfg->cd.asid) |
>>> - CTXDESC_CD_0_V;
>>> + u64 val;
>>> + bool cd_live;
>>> + struct arm_smmu_device *smmu = smmu_domain->smmu;
>>> + __le64 *cdptr = smmu_domain->s1_cfg.table.ptr + ssid *
>>> + CTXDESC_CD_DWORDS;>
>>> - /* STALL_MODEL==0b10 && CD.S==0 is ILLEGAL */
>>> - if (smmu->features & ARM_SMMU_FEAT_STALL_FORCE)
>>> - val |= CTXDESC_CD_0_S;
>>> + val = le64_to_cpu(cdptr[0]);
>>> + cd_live = !!(val & CTXDESC_CD_0_V);
>>>
>>> - cdptr[0] = cpu_to_le64(val);
>>> + if (!cd) { /* (4) */
>>> + val = 0;
>>> + } else if (cd_live) { /* (3) */
>>> + val &= ~CTXDESC_CD_0_ASID;
>>> + val |= FIELD_PREP(CTXDESC_CD_0_ASID, cd->asid);
>>> + /*
>>> + * Until CD+TLB invalidation, both ASIDs may be used for tagging
>>> + * this substream's traffic
>>> + */
>>> + } else { /* (1) and (2) */
>>> + cdptr[1] = cpu_to_le64(cd->ttbr & CTXDESC_CD_1_TTB0_MASK);
>>> + cdptr[2] = 0;
>>> + cdptr[3] = cpu_to_le64(cd->mair);
>>> +
>>> + /*
>>> + * STE is live, and the SMMU might fetch this CD at any
>>> + * time. Ensure that it observes the rest of the CD before we
>>> + * enable it.
>> Mostly, on't you want the invalid state to be seen?
Sorry I wanted to say you mostly want to enforce the INVALID bit (what I
understand from your below explanations). I was confused by the wording
"Ensure that it observes the rest of the CD before we enable it".
>
> Sorry I didn't get your question. Without the sync, the SMMU could read an
> invalid address in CD[1], read V=1 in CD[0] and proceed with dereferencing
> the bogus pointer before seeing our update to CD[1].
>
> To prevent this we follow the update procedure described in IHI0070Ca
> 3.21.3.1 (Configuration structure update procedure):
>
> Because the SMMU can read any reachable structure at any time, and is not
> required to read the double-words of the structure in order, Arm
> recommends that the following procedure is used to initialize structures:
> 1. Structure starts invalid, having V == 0.
> 2. Fill in all fields, leaving V == 0, then perform a DSB operation to
> ensure written data is observable from the SMMU.
> 3. Issue a CMD_CFGI_<STRUCT>, as appropriate.
> 4. Issue a CMD_SYNC, and wait for completion.
> 5. Set V to 1, then perform a DSB operation to ensure write is
> observable by the SMMU.
> 6. Issue CMD_CFGI_<STRUCT>, as appropriate.
> 7. Optionally issue a CMD_SYNC, and wait for completion. This must be
> done if a subsequent software operation, such as enabling device
> DMA, depends on the SMMU using the new structure.
>
>>> @@ -1664,6 +1739,7 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_master *master, u32 sid,
>>> if (s1_cfg) {
>>> BUG_ON(ste_live);
>>> dst[1] = cpu_to_le64(
>>> + FIELD_PREP(STRTAB_STE_1_S1DSS,
>>> STRTAB_STE_1_S1DSS_SSID0) |
>>> FIELD_PREP(STRTAB_STE_1_S1CIR,
>>> STRTAB_STE_1_S1C_CACHE_WBRA) |
>>> FIELD_PREP(STRTAB_STE_1_S1COR,
>>> STRTAB_STE_1_S1C_CACHE_WBRA) |
>>> FIELD_PREP(STRTAB_STE_1_S1CSH, ARM_SMMU_SH_ISH) |
>>> @@ -1674,7 +1750,9 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_master *master, u32 sid,
>>> dst[1] |= cpu_to_le64(STRTAB_STE_1_S1STALLD);
>>>
>>> val |= (s1_cfg->table.ptr_dma & STRTAB_STE_0_S1CTXPTR_MASK) |
>>> - FIELD_PREP(STRTAB_STE_0_CFG, STRTAB_STE_0_CFG_S1_TRANS);
>>> + FIELD_PREP(STRTAB_STE_0_CFG, STRTAB_STE_0_CFG_S1_TRANS)
>>> |
>>> + FIELD_PREP(STRTAB_STE_0_S1CDMAX, s1_cfg->s1cdmax) |
>>> + FIELD_PREP(STRTAB_STE_0_S1FMT, s1_cfg->s1fmt);
>> Do I understand correctly that each time we update the CD, we also
>> update the STE. This is not wrong but theoretically this is not needed,
>> right?
>
> Only the primary CD. Once we add SVA (or auxiliary domains) we need to
> update secondary CDs while the STE is live. This series is just
> preparation for SVA support. I didn't include the full support because it
> requires another 25+ patches.
OK
>
>> This also explains why you do not need the CMD_PREFETCH_CONFIG with ssid
>> because you invalidate the config per sid?
>
> Hm, I didn't add a CMD_PREFETCH_CONFIG to CDs because I don't know if it's
> useful. Maybe as future optimization.
OK
Thanks
Eric
>
> Thanks,
> Jean
>
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