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.Xiao at amd.com>; Kuehling, Felix >>> <Felix.Kuehling at amd.com>; Christian König >>> <ckoenig.leichtzumerken at gmail.com>; amd-gfx at 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-bounces at lists.freedesktop.org> On Behalf Of >>>> Felix Kuehling >>>> Sent: Tuesday, August 28, 2018 3:03 AM >>>> To: Christian König <ckoenig.leichtzumerken at gmail.com>; >>>> amd-gfx at lists.freedesktop.org; Koenig, Christian >>>> <Christian.Koenig at 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.Kuehling at 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.koenig at 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 at lists.freedesktop.org >>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx > _______________________________________________ > amd-gfx mailing list > amd-gfx at lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/amd-gfx
