linux-kernel - Re: [PATCH v2 07/10] drm/msm/gem: Rework vma lookup and pin

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Message-ID: <8b1aa75d-1de4-40d2-c80b-7d23605dd49e@collabora.com>
Date:   Thu, 31 Mar 2022 23:49:27 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Rob Clark <robdclark@...il.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 07/10] drm/msm/gem: Rework vma lookup and pin

On 3/31/22 21:58, Rob Clark wrote:
> On Thu, Mar 31, 2022 at 11:27 AM Dmitry Osipenko
> <dmitry.osipenko@...labora.com> wrote:
>>
>> On 3/30/22 23:47, Rob Clark wrote:
>>> From: Rob Clark <robdclark@...omium.org>
>>>
>>> Combines duplicate vma lookup in the get_and_pin path.
>>>
>>> Signed-off-by: Rob Clark <robdclark@...omium.org>
>>> ---
>>>  drivers/gpu/drm/msm/msm_gem.c | 50 ++++++++++++++++++-----------------
>>>  1 file changed, 26 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
>>> index deafae6feaa8..218744a490a4 100644
>>> --- a/drivers/gpu/drm/msm/msm_gem.c
>>> +++ b/drivers/gpu/drm/msm/msm_gem.c
>>> @@ -376,39 +376,40 @@ put_iova_vmas(struct drm_gem_object *obj)
>>>       }
>>>  }
>>>
>>> -static int get_iova_locked(struct drm_gem_object *obj,
>>> -             struct msm_gem_address_space *aspace, uint64_t *iova,
>>> +static struct msm_gem_vma *get_vma_locked(struct drm_gem_object *obj,
>>> +             struct msm_gem_address_space *aspace,
>>>               u64 range_start, u64 range_end)
>>>  {
>>>       struct msm_gem_vma *vma;
>>> -     int ret = 0;
>>>
>>>       GEM_WARN_ON(!msm_gem_is_locked(obj));
>>>
>>>       vma = lookup_vma(obj, aspace);
>>>
>>>       if (!vma) {
>>> +             int ret;
>>> +
>>>               vma = add_vma(obj, aspace);
>>>               if (IS_ERR(vma))
>>> -                     return PTR_ERR(vma);
>>> +                     return vma;
>>>
>>>               ret = msm_gem_init_vma(aspace, vma, obj->size,
>>>                       range_start, range_end);
>>>               if (ret) {
>> You're allocation range_start -> range_end
>>
>>
>>>                       del_vma(vma);
>>> -                     return ret;
>>> +                     return ERR_PTR(ret);
>>>               }
>>> +     } else {
>>> +             GEM_WARN_ON(vma->iova < range_start);
>>> +             GEM_WARN_ON((vma->iova + obj->size) > range_end);
>>
>> and then comparing range_start -> range_start + obj->size, hence you're
>> assuming that range_end always equals to obj->size during the allocation.
>>
>> I'm not sure what is the idea here.. this looks inconsistent. I think
>> you wanted to write:
>>
>>                 GEM_WARN_ON(vma->iova < range_start);
>>                 GEM_WARN_ON(vma->iova + (vma->node.size << PAGE_SHIFT) > range_end);
>>
>> But is it really useful to check whether the new range is inside of the
>> old range? Shouldn't it be always a error to change the IOVA range
>> without reallocating vma?
> 
> There are a few cases (for allocations for GMU) where the range is
> larger than the bo.. see a6xx_gmu_memory_alloc()

Ahh, I didn't read the code properly and see now why you're using the
obj->size. It's the range where you want to put the BO. Looks good then.

Reviewed-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>