linux-kernel - Re: [PATCH v14 12/17] drm/radeon, arm64: untag user pointers

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Message-ID: <bfe5e11e-6dc4-352f-57eb-d527f965a2ef@amd.com>
Date:   Tue, 30 Apr 2019 17:57:12 +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 12/17] drm/radeon, 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.
>
> radeon_ttm_tt_pin_userptr() uses provided user pointers for vma
> lookups, which can only by done with untagged pointers. This patch
> untags user pointers when they are being set in
> radeon_ttm_tt_pin_userptr().
>
> In amdgpu_gem_userptr_ioctl() 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 untags user pointers in radeon_gem_userptr_ioctl().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>   drivers/gpu/drm/radeon/radeon_gem.c | 2 ++
>   drivers/gpu/drm/radeon/radeon_ttm.c | 2 +-
>   2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c
> index 44617dec8183..90eb78fb5eb2 100644
> --- a/drivers/gpu/drm/radeon/radeon_gem.c
> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> @@ -291,6 +291,8 @@ int radeon_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/radeon/radeon_ttm.c b/drivers/gpu/drm/radeon/radeon_ttm.c
> index 9920a6fc11bf..dce722c494c1 100644
> --- a/drivers/gpu/drm/radeon/radeon_ttm.c
> +++ b/drivers/gpu/drm/radeon/radeon_ttm.c
> @@ -742,7 +742,7 @@ int radeon_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, because you already untagged the 
address in the only caller of this function in radeon_gem_userptr_ioctl. 
The change there will affect both the userptr and MMU notifier setup and 
makes sure that both are in sync, using the same untagged address.

Regards,
   Felix


>          gtt->usermm = current->mm;
>          gtt->userflags = flags;
>          return 0;
> --
> 2.21.0.593.g511ec345e18-goog
>