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Date: Mon, 13 May 2019 12:43:46 +0100
From: Robin Murphy <robin.murphy@....com>
To: Auger Eric <eric.auger@...hat.com>, eric.auger.pro@...il.com,
iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu, joro@...tes.org,
alex.williamson@...hat.com, jacob.jun.pan@...ux.intel.com,
yi.l.liu@...el.com, jean-philippe.brucker@....com,
will.deacon@....com
Cc: kevin.tian@...el.com, ashok.raj@...el.com, marc.zyngier@....com,
christoffer.dall@....com, peter.maydell@...aro.org,
vincent.stehle@....com
Subject: Re: [PATCH v7 12/23] iommu/smmuv3: Get prepared for nested stage
support
On 10/05/2019 15:34, Auger Eric wrote:
> Hi Robin,
>
> On 5/8/19 4:24 PM, Robin Murphy wrote:
>> On 08/04/2019 13:19, Eric Auger wrote:
>>> To allow nested stage support, we need to store both
>>> stage 1 and stage 2 configurations (and remove the former
>>> union).
>>>
>>> A nested setup is characterized by both s1_cfg and s2_cfg
>>> set.
>>>
>>> We introduce a new ste.abort field that will be set upon
>>> guest stage1 configuration passing. If s1_cfg is NULL and
>>> ste.abort is set, traffic can't pass. If ste.abort is not set,
>>> S1 is bypassed.
>>>
>>> arm_smmu_write_strtab_ent() is modified to write both stage
>>> fields in the STE and deal with the abort field.
>>>
>>> In nested mode, only stage 2 is "finalized" as the host does
>>> not own/configure the stage 1 context descriptor, guest does.
>>>
>>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>>>
>>> ---
>>>
>>> v4 -> v5:
>>> - reset ste.abort on detach
>>>
>>> v3 -> v4:
>>> - s1_cfg.nested_abort and nested_bypass removed.
>>> - s/ste.nested/ste.abort
>>> - arm_smmu_write_strtab_ent modifications with introduction
>>> of local abort, bypass and translate local variables
>>> - comment updated
>>>
>>> v1 -> v2:
>>> - invalidate the STE before moving from a live STE config to another
>>> - add the nested_abort and nested_bypass fields
>>> ---
>>> drivers/iommu/arm-smmu-v3.c | 35 ++++++++++++++++++++---------------
>>> 1 file changed, 20 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>>> index 21d027695181..e22e944ffc05 100644
>>> --- a/drivers/iommu/arm-smmu-v3.c
>>> +++ b/drivers/iommu/arm-smmu-v3.c
>>> @@ -211,6 +211,7 @@
>>> #define STRTAB_STE_0_CFG_BYPASS 4
>>> #define STRTAB_STE_0_CFG_S1_TRANS 5
>>> #define STRTAB_STE_0_CFG_S2_TRANS 6
>>> +#define STRTAB_STE_0_CFG_NESTED 7
>>> #define STRTAB_STE_0_S1FMT GENMASK_ULL(5, 4)
>>> #define STRTAB_STE_0_S1FMT_LINEAR 0
>>> @@ -514,6 +515,7 @@ struct arm_smmu_strtab_ent {
>>> * configured according to the domain type.
>>> */
>>> bool assigned;
>>> + bool abort;
>>> struct arm_smmu_s1_cfg *s1_cfg;
>>> struct arm_smmu_s2_cfg *s2_cfg;
>>> };
>>> @@ -628,10 +630,8 @@ struct arm_smmu_domain {
>>> bool non_strict;
>>> enum arm_smmu_domain_stage stage;
>>> - union {
>>> - struct arm_smmu_s1_cfg s1_cfg;
>>> - struct arm_smmu_s2_cfg s2_cfg;
>>> - };
>>> + struct arm_smmu_s1_cfg s1_cfg;
>>> + struct arm_smmu_s2_cfg s2_cfg;
>>> struct iommu_domain domain;
>>> @@ -1108,12 +1108,13 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_device *smmu, u32 sid,
>>> __le64 *dst, struct arm_smmu_strtab_ent *ste)
>>> {
>>> /*
>>> - * This is hideously complicated, but we only really care about
>>> - * three cases at the moment:
>>> + * We care about the following transitions:
>>> *
>>> * 1. Invalid (all zero) -> bypass/fault (init)
>>> - * 2. Bypass/fault -> translation/bypass (attach)
>>> - * 3. Translation/bypass -> bypass/fault (detach)
>>> + * 2. Bypass/fault -> single stage translation/bypass (attach)
>>> + * 3. single stage Translation/bypass -> bypass/fault (detach)
>>> + * 4. S2 -> S1 + S2 (attach_pasid_table)
>>> + * 5. S1 + S2 -> S2 (detach_pasid_table)
>>> *
>>> * Given that we can't update the STE atomically and the SMMU
>>> * doesn't read the thing in a defined order, that leaves us
>>> @@ -1124,7 +1125,7 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_device *smmu, u32 sid,
>>> * 3. Update Config, sync
>>> */
>>> u64 val = le64_to_cpu(dst[0]);
>>> - bool ste_live = false;
>>> + bool abort, bypass, translate, ste_live = false;
>>> struct arm_smmu_cmdq_ent prefetch_cmd = {
>>> .opcode = CMDQ_OP_PREFETCH_CFG,
>>> .prefetch = {
>>> @@ -1138,11 +1139,11 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_device *smmu, u32 sid,
>>> break;
>>> case STRTAB_STE_0_CFG_S1_TRANS:
>>> case STRTAB_STE_0_CFG_S2_TRANS:
>>> + case STRTAB_STE_0_CFG_NESTED:
>>> ste_live = true;
>>> break;
>>> case STRTAB_STE_0_CFG_ABORT:
>>> - if (disable_bypass)
>>> - break;
>>> + break;
>>> default:
>>> BUG(); /* STE corruption */
>>> }
>>> @@ -1152,8 +1153,13 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_device *smmu, u32 sid,
>>> val = STRTAB_STE_0_V;
>>> /* Bypass/fault */
>>> - if (!ste->assigned || !(ste->s1_cfg || ste->s2_cfg)) {
>>> - if (!ste->assigned && disable_bypass)
>>> +
>>> + abort = (!ste->assigned && disable_bypass) || ste->abort;
>>> + translate = ste->s1_cfg || ste->s2_cfg;
>>> + bypass = !abort && !translate;
>>> +
>>> + if (abort || bypass) {
>>> + if (abort)
>>> val |= FIELD_PREP(STRTAB_STE_0_CFG,
>>> STRTAB_STE_0_CFG_ABORT);
>>> else
>>> val |= FIELD_PREP(STRTAB_STE_0_CFG,
>>> STRTAB_STE_0_CFG_BYPASS);
>>> @@ -1172,7 +1178,6 @@ static void arm_smmu_write_strtab_ent(struct
>>> arm_smmu_device *smmu, u32 sid,
>>> }
>>> if (ste->s1_cfg) {
>>> - BUG_ON(ste_live);
>>
>> Hmm, I'm a little uneasy about just removing these checks altogether, as
>> there are still cases where rewriting a live entry is bogus, that we'd
>> really like to keep catching. Is the problem that it's hard to tell when
>> you're 'rewriting' the S2 config of a nested entry with the same thing
>> on attaching/detaching its S1 context?
> No, I restored the original checks in !nested mode and added a new check
> to make sure we never update a live S1 in nested mode. Only S2 can be live.
Right, either way it's fairly easy to enforce "!(cfg->s1 && ste->s1)",
but what I'm really concerned about is that fact where Stream IDs (or
possibly PASIDS) get messed up and we end up silently writing a nested
config over an STE which happens to already have an S2 configuration for
some other domain (or vice versa).
I guess it might suffice to verify that the VTTBRs match for S2<->nested
transitions, what do you reckon?
Robin.
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