Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <368b9b1b7343e35b446bb1028ccf0ae75dc2adc4.camel@mengyan1223.wang>
Subject: Re: [PATCH] drm/amdgpu: fix an underflow on non-4KB-page systems
From:   Xi Ruoyao <xry111@mengyan1223.wang>
To:     Christian =?ISO-8859-1?Q?K=F6nig?= 
        <ckoenig.leichtzumerken@gmail.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Christian =?ISO-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>
Cc:     David Airlie <airlied@linux.ie>,
        Felix Kuehling <Felix.Kuehling@amd.com>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Dan =?ISO-8859-1?Q?Hor=E1k?= <dan@danny.cz>,
        amd-gfx@lists.freedesktop.org, Daniel Vetter <daniel@ffwll.ch>,
        stable@vger.kernel.org
Date:   Tue, 30 Mar 2021 03:40:04 +0800
In-Reply-To: <7701fb71-9243-2d90-e1e1-d347a53b7d77@gmail.com>
References: <20210329175348.26859-1-xry111@mengyan1223.wang>
         <d192e2a8-8baf-0a8c-93a9-9abbad992c7d@gmail.com>
         <be9042b9294bda450659d3cd418c5e8759d57319.camel@mengyan1223.wang>
         <9a11c873-a362-b5d1-6d9c-e937034e267d@gmail.com>
         <bf9e05d4a6ece3e8bf1f732b011d3e54bbf8000e.camel@mengyan1223.wang>
         <84b3911173ad6beb246ba0a77f93d888ee6b393e.camel@mengyan1223.wang>
         <97c520ce107aa4d5fd96e2c380c8acdb63d45c37.camel@mengyan1223.wang>
         <7701fb71-9243-2d90-e1e1-d347a53b7d77@gmail.com>
Content-Type: text/plain; charset="UTF-8"
User-Agent: Evolution 3.40.0 
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 2021-03-29 21:36 +0200, Christian König wrote:
> Am 29.03.21 um 21:27 schrieb Xi Ruoyao:
> > Hi Christian,
> > 
> > I don't think there is any constraint implemented to ensure `num_entries %
> > AMDGPU_GPU_PAGES_IN_CPU_PAGE == 0`.  For example, in `amdgpu_vm_bo_map()`:
> > 
> >          /* validate the parameters */
> >          if (saddr & AMDGPU_GPU_PAGE_MASK || offset & AMDGPU_GPU_PAGE_MASK
> > ||
> >              size == 0 || size & AMDGPU_GPU_PAGE_MASK)
> >                  return -EINVAL;
> > 
> > /* snip */
> > 
> >          saddr /= AMDGPU_GPU_PAGE_SIZE;
> >          eaddr /= AMDGPU_GPU_PAGE_SIZE;
> > 
> > /* snip */
> > 
> >          mapping->start = saddr;
> >          mapping->last = eaddr;
> > 
> > 
> > If we really want to ensure (mapping->last - mapping->start + 1) %
> > AMDGPU_GPU_PAGES_IN_CPU_PAGE == 0, then we should replace
> > "AMDGPU_GPU_PAGE_MASK"
> > in "validate the parameters" with "PAGE_MASK".
> 
> Yeah, good point.
> 
> > I tried it and it broke userspace: Xorg startup fails with EINVAL with this
> > change.
> 
> Well in theory it is possible that we always fill the GPUVM on a 4k 
> basis while the native page size of the CPU is larger. Let me double 
> check the code.
> 
> BTW: What code base are you based on? The code your post here is quite 
> outdated.

Linus' tree.

I'll go to sleep now (it's 03:39 here :( ), when I wake up I can try to fetch
drm-next or something.
-- 
Xi Ruoyao <xry111@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University