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Date: Mon, 13 May 2019 16:40:41 +0200
From: Auger Eric <eric.auger@...hat.com>
To: Robin Murphy <robin.murphy@....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
Hi Robin,
On 5/13/19 1:43 PM, Robin Murphy wrote:
> 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?
Yes I can test the STE.S2TTB values which should are identical during
such transitions.
Thanks
Eric
>
> Robin.
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