linux-kernel - Re: [PATCH v14 11/17] drm/amdgpu, arm64: untag user pointers

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Date:   Tue, 30 Apr 2019 18:03:12 +0000
From:   "Kuehling, Felix" <Felix.Kuehling@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        "Kuehling@...gle.com" <Kuehling@...gle.com>,
        "Deucher@...gle.com" <Deucher@...gle.com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "Koenig@...gle.com" <Koenig@...gle.com>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v14 11/17] drm/amdgpu, arm64: untag user pointers

On 2019-04-30 9:25 a.m., Andrey Konovalov wrote:
> [CAUTION: External Email]
>
> This patch is a part of a series that extends arm64 kernel ABI to allow to
> pass tagged user pointers (with the top byte set to something else other
> than 0x00) as syscall arguments.
>
> amdgpu_ttm_tt_get_user_pages() uses provided user pointers for vma
> lookups, which can only by done with untagged pointers. This patch
> untag user pointers when they are being set in
> amdgpu_ttm_tt_set_userptr().
>
> In amdgpu_gem_userptr_ioctl() and amdgpu_amdkfd_gpuvm.c/init_user_pages()
> an MMU notifier is set up with a (tagged) userspace pointer. The untagged
> address should be used so that MMU notifiers for the untagged address get
> correctly matched up with the right BO. This patch untag user pointers in
> amdgpu_gem_userptr_ioctl() for the GEM case and in
> amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu() for the KFD case.
>
> Suggested-by: Kuehling, Felix <Felix.Kuehling@....com>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 2 +-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c          | 2 ++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c          | 2 +-
>   3 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> index 1921dec3df7a..20cac44ed449 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> @@ -1121,7 +1121,7 @@ int amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu(
>                  alloc_flags = 0;
>                  if (!offset || !*offset)
>                          return -EINVAL;
> -               user_addr = *offset;
> +               user_addr = untagged_addr(*offset);
>          } else if (flags & ALLOC_MEM_FLAGS_DOORBELL) {
>                  domain = AMDGPU_GEM_DOMAIN_GTT;
>                  alloc_domain = AMDGPU_GEM_DOMAIN_CPU;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> index d21dd2f369da..985cb82b2aa6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
> @@ -286,6 +286,8 @@ int amdgpu_gem_userptr_ioctl(struct drm_device *dev, void *data,
>          uint32_t handle;
>          int r;
>
> +       args->addr = untagged_addr(args->addr);
> +
>          if (offset_in_page(args->addr | args->size))
>                  return -EINVAL;
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 73e71e61dc99..1d30e97ac2c4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -1248,7 +1248,7 @@ int amdgpu_ttm_tt_set_userptr(struct ttm_tt *ttm, uint64_t addr,
>          if (gtt == NULL)
>                  return -EINVAL;
>
> -       gtt->userptr = addr;
> +       gtt->userptr = untagged_addr(addr);

Doing this here seems unnecessary. You already untagged the address in 
both callers of this function. Untagging in the two callers ensures that 
the userptr and MMU notifier are in sync, using the same untagged 
address. Doing it again here is redundant.

Regards,
   Felix


>          gtt->userflags = flags;
>
>          if (gtt->usertask)
> --
> 2.21.0.593.g511ec345e18-goog
>