Can you explain what the benefits can be gained from AGP aperture enablement? Otherwise, it would increase our maintenance workload.
Regards, Jack -----Original Message----- From: Christian König <ckoenig.leichtzumer...@gmail.com> Sent: Wednesday, August 29, 2018 4:47 PM To: Kuehling, Felix <felix.kuehl...@amd.com>; Koenig, Christian <christian.koe...@amd.com>; Xiao, Jack <jack.x...@amd.com>; amd-gfx@lists.freedesktop.org Subject: Re: [PATCH 01/10] drm/amdgpu: use only the lower address space on GMC9 Completely agree with Felix here. It makes system memory access slightly simpler, but I would say that you accidentally corrupt the GART table and that you accidentally corrupt the the AGP aperture is equally likely. Regards, Christian. Am 28.08.2018 um 20:12 schrieb Felix Kuehling: > The GPU always has access to the entire guest physical address space. > You can just program arbitrary addresses into page table entries and > set the system bit. That's how GART and GPUVM mappings work. They will > not go through the AGP aperture. And there is no mechanism (other than > an > IOMMU) to protect system memory from GPU access. > > Regards, > Felix > > > On 2018-08-28 07:41 AM, Christian König wrote: >> Well that is indeed true, but we still have IOMMU between the GPU and >> the system memory. >> >> So we should still catch issues when something goes terrible wrong. >> >> Additional to that only the system domain, e.g. kernel copies, page >> table updates etc are allowed to use it. >> >> Regards, >> Christian. >> >> Am 28.08.2018 um 09:06 schrieb Xiao, Jack: >>> I mean it has risk to make GPU allowed to access to most system >>> memory without explicit claiming, it's easier to mask problem. >>> >>> Regards, >>> Jack >>> >>> -----Original Message----- >>> From: Koenig, Christian >>> Sent: Tuesday, August 28, 2018 2:46 PM >>> To: Xiao, Jack <jack.x...@amd.com>; Kuehling, Felix >>> <felix.kuehl...@amd.com>; Christian König >>> <ckoenig.leichtzumer...@gmail.com>; amd-gfx@lists.freedesktop.org >>> Subject: Re: [PATCH 01/10] drm/amdgpu: use only the lower address >>> space on GMC9 >>> >>>> This series patches seems to make AGP aperture allowed to access >>>> any system memory (16GB) bypass GPU VM protection. >>> The system aperture should only be active in the system domain, or >>> otherwise applications would have access to local memory as well. >>> >>> There are some bits in the VM registers to enable/disable that, but >>> when we would have that setting incorrect we would see quite a bunch >>> of other problems. >>> >>> Might still be a good idea to double check if all the bits are setup >>> correctly. >>> >>> Regards, >>> Christian. >>> >>> Am 28.08.2018 um 07:31 schrieb Xiao, Jack: >>>> This series patches seems to make AGP aperture allowed to access >>>> any system memory (16GB) bypass GPU VM protection. >>>> If someone made a wrong logic requesting an illegal address which >>>> occasionally was located inside AGP aperture, but without any VM >>>> protection, the illegal address would be finally translated into a >>>> system memory address; if GPU read/wrote such system memory >>>> address, the system memory address might belong to kernel or any >>>> user application, the r/w operation would result in any unpredictable >>>> issue. >>>> The most important is that such kind of issue is so hard to be >>>> addressed. >>>> Is it worth doing this, but exposing risk? >>>> >>>> Regards, >>>> Jack >>>> >>>> -----Original Message----- >>>> From: amd-gfx <amd-gfx-boun...@lists.freedesktop.org> On Behalf Of >>>> Felix Kuehling >>>> Sent: Tuesday, August 28, 2018 3:03 AM >>>> To: Christian König <ckoenig.leichtzumer...@gmail.com>; >>>> amd-gfx@lists.freedesktop.org; Koenig, Christian >>>> <christian.koe...@amd.com> >>>> Subject: Re: [PATCH 01/10] drm/amdgpu: use only the lower address >>>> space on GMC9 >>>> >>>> The point of this series seems to be to allow access to small >>>> system memory BOs (one page) without a GART mapping. I'm guessing >>>> that reduces pressure on the GART and removes the need for HDP and >>>> TLB flushes. Why does Patch 10 only enable that on GFXv9? Is there >>>> less benefit on older chips? >>>> >>>> Is this related to your recent changes to allow page tables in >>>> system memory? >>>> >>>> See my replies to patch 6 and 8. Other than that, the series is >>>> Acked-by: Felix Kuehling <felix.kuehl...@amd.com> >>>> >>>> Regards, >>>> Felix >>>> >>>> >>>> On 2018-08-27 12:53 PM, Christian König wrote: >>>>> Only use the lower address space on GMC9 for the system domain. >>>>> Otherwise we would need to sign extend GMC addresses. >>>>> >>>>> Signed-off-by: Christian König <christian.koe...@amd.com> >>>>> --- >>>>> drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c | 7 +++---- >>>>> 1 file changed, 3 insertions(+), 4 deletions(-) >>>>> >>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c >>>>> b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c >>>>> index e44b5191735d..d982956c8329 100644 >>>>> --- a/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c >>>>> +++ b/drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c >>>>> @@ -938,11 +938,10 @@ static int gmc_v9_0_sw_init(void *handle) >>>>> if (r) >>>>> return r; >>>>> - /* Set the internal MC address mask >>>>> - * This is the max address of the GPU's >>>>> - * internal address space. >>>>> + /* Use only the lower range for the internal MC address mask. >>>>> This is >>>>> + * the max address of the GPU's internal address space. >>>>> */ >>>>> - adev->gmc.mc_mask = 0xffffffffffffULL; /* 48 bit MC */ >>>>> + adev->gmc.mc_mask = 0x7fffffffffffULL; >>>>> /* set DMA mask + need_dma32 flags. >>>>> * PCIE - can handle 44-bits. >>>> _______________________________________________ >>>> amd-gfx mailing list >>>> amd-gfx@lists.freedesktop.org >>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx > _______________________________________________ > amd-gfx mailing list > amd-gfx@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/amd-gfx _______________________________________________ amd-gfx mailing list amd-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/amd-gfx