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.
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