[PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Fri Jan 18 12:20:44 UTC 2019

You know what, …  when you explained range 0 to HOLE-START is even not good to exposed to UMD I thought you made a typo and that’s why I repeat my question again …
Sorry my fault then. Didn't wanted to sound offending.

it’s the first time I heard that GMC9  cannot use 0 -> HOLE-START even for UMD general usage …
Well you actually can do it, but then you can't use the ATC or other SVA mechanism.

With your assert in DEV_INFO the “virtual_address_offset/max” is now *totally* wrong … I saw current kmd still give that range from 0 to HOLE_START
That is actually correct and for backward compatibility with old userspace. But since old userspace won't use the ATC that is also not a problem.

As I said one possibility to solve this issue would be to use a low CSA address for SRIOV, because the ATC isn't usable with SRIOV anyway.

I would just like to avoid that because it sounds like the CSA for some reason doesn't work at all in the higher address range and we will certainly then run into issues with that on bare metal as well.

I need to check what you said with some HW guys, that sounds crazy …
Actually that's not so crazy at all. See the ATC uses the CPU page tables to provide parts of the virtual GPU address space.

E.g. when it is enabled you can then use the same pointer to memory on the CPU and the GPU.

The problem is when the UMD now manually maps something into this range you can have a clash of the address space and the MC doesn't know any more if it should send a request to the CPU or the GPU page tables.

Regards,
Christian.

Am 18.01.19 um 11:57 schrieb Liu, Monk:
You know what, …  when you explained range 0 to HOLE-START is even not good to exposed to UMD I thought you made a typo and that’s why I repeat my question again …
it’s the first time I heard that GMC9  cannot use 0 -> HOLE-START even for UMD general usage …
With your assert in DEV_INFO the “virtual_address_offset/max” is now *totally* wrong … I saw current kmd still give that range from 0 to HOLE_START
I need to check what you said with some HW guys, that sounds crazy …

/Monk
From: Christian König <ckoenig.leichtzumerken at gmail.com><mailto:ckoenig.leichtzumerken at gmail.com>
Sent: Friday, January 18, 2019 5:12 PM
To: Liu, Monk <Monk.Liu at amd.com><mailto:Monk.Liu at amd.com>; Koenig, Christian <Christian.Koenig at amd.com><mailto:Christian.Koenig at amd.com>; Lou, Wentao <Wentao.Lou at amd.com><mailto:Wentao.Lou at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>; Zhu, Rex <Rex.Zhu at amd.com><mailto:Rex.Zhu at amd.com>
Cc: Deng, Emily <Emily.Deng at amd.com><mailto:Emily.Deng at amd.com>
Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Hi Monk,

You see that for UMD, it can use 0 to HOLE_START
Let me say it once more: The UMD nor anybody else CAN'T use 0 to HOLE_START, that region is reserved for the ATC hardware!

We unfortunately didn't knew that initially and also didn't used the ATC, so we didn't ran into a problem.

But ROCm now uses the ATC on Raven/Picasso and I have a branch where I enable it on Vega as well. So when we don't fix that we will run into problems here.

The ATC isn't usable in combination with SRIOV and I don't think Windows uses it either, so they probably never ran into any issues.

Do you mean even UMD should  not use virtual address that dropped in range from 0 to HOLE_START ?
Yes, exactly! That in combination with ATC use can have quite a bunch of strange and hard to track down effects because two parts of the driver are using the same address space.

That way where should UMD work in ?and I assume our UMD now still using this range, this part make me puzzle
At least Mesa now uses the high address space from HOLE_END..0xFFFF FFFF FFFF FFFF.

Regards,
Christian.

Am 18.01.19 um 02:32 schrieb Liu, Monk:
Thanks Christian,

Questions I have now:

  1.  You see that for UMD, it can use 0 to HOLE_START, so why CSA cannot use that range although the range is as you said reserved to ATC h/w ? Be note that for windows KMD, the CSA is allocated by UMD driver so CSA shares the same aperture /space range with other UMD BO, which mean CSA in windows also located in ATC range, if that’s a problem why windows still works well.

     *   Can you illustrate this limitation with more details ? we need to understand why CSA couldn’t be put in ATC range.

  1.  According to your previous description :” Now on Vega/Raven/Picasso etc.. (everything with a GFX9) the lower range (0x0-0x8000 0000 0000) is reserved for SVA/ATC use. Since we unfortunately didn't knew that initially we exposed those to older user space as usable and also put the CSA in there.”

     *   Do you mean even UMD should  not use virtual address that dropped in range from 0 to HOLE_START ?

that way where should UMD work in ?and I assume our UMD now still using this range, this part make me puzzle

/Monk
From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org><mailto:amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Koenig, Christian
Sent: Thursday, January 17, 2019 9:26 PM
To: Liu, Monk <Monk.Liu at amd.com><mailto:Monk.Liu at amd.com>; Lou, Wentao <Wentao.Lou at amd.com><mailto:Wentao.Lou at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>; Zhu, Rex <Rex.Zhu at amd.com><mailto:Rex.Zhu at amd.com>
Cc: Deng, Emily <Emily.Deng at amd.com><mailto:Emily.Deng at amd.com>
Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Hi Monk,

Regarding with above sentence, do you mean this range (0->HOLE_START) shouldn’t be exposed to user space ? I don’t get your point here …
Yes exactly. As I said the problem is that 0->HOLE_START is reserved for the ATC hardware, we should not touch it at all.

Putting CSA in 0~HOLD_START is the legacy approach we selected for a long time since very early stage, how comes that you think it is a problem now ?
That turned out to be never a good idea in the first place.

What we could do is reduce the max_pfn for SRIOV because the ATC doesn't work in that configuration anyway. But I would only do this as last resort.

Any idea why an address above the hole doesn't work with SRIOV? It seems to work fine in the bare metal case.

Regards,
Christian.

Am 17.01.19 um 14:19 schrieb Liu, Monk:
Hi Christian

Thanks for explaining the HOLD for us,

My understanding is we still could put CSA to 0~HOLE_START, because we can report UMD the max space is HOLD_START-CSA_SIZE , thus no colliding will hit.

> Now on Vega/Raven/Picasso etc.. (everything with a GFX9) the lower range (0x0-0x8000 0000 0000) is reserved for SVA/ATC use. Since we unfortunately didn't knew that initially we exposed those to older userspace as usable and also put the CSA in there.

Regarding with above sentence, do you mean this range (0->HOLE_START) shouldn’t be exposed to user space ? I don’t get your point here …

Putting CSA in 0~HOLD_START is the legacy approach we selected for a long time since very early stage, how comes that you think it is a problem now ?

/Monk
From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org><mailto:amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Koenig, Christian
Sent: Thursday, January 17, 2019 4:30 PM
To: Liu, Monk <Monk.Liu at amd.com><mailto:Monk.Liu at amd.com>; Lou, Wentao <Wentao.Lou at amd.com><mailto:Wentao.Lou at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>; Zhu, Rex <Rex.Zhu at amd.com><mailto:Rex.Zhu at amd.com>
Cc: Deng, Emily <Emily.Deng at amd.com><mailto:Emily.Deng at amd.com>
Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Hi Monk,

ok let me explain a bit more how the hardware works.

The GMC manages a virtual 64bit address space, but only 48bit of that virtual address space are handled by the page table walker.

The 48bits of address space are sign extended, so bit 47 of that are extended into bits 48-63.

This gives us the following memory layout:
0x0
.... virtual address space
0x8000 0000 0000
.... hole
0xFFFF 8000 0000 0000
.... virtual address space
0xFFFF FFFF FFFF FFFF

Trying to access the hole results in a range fault interrupt IIRC.

When doing the VM page table walk the topmost 16bits are ignored, so when programming the page table walker you cut those of and use a linear address again. This is what AMDGPU_GMC_HOLE_MASK is good for.

Now on Vega/Raven/Picasso etc.. (everything with a GFX9) the lower range (0x0-0x8000 0000 0000) is reserved for SVA/ATC use. Since we unfortunately didn't knew that initially we exposed those to older userspace as usable and also put the CSA in there.

The most likely cause of this is that we still have a bug somewhere about this, e.g. not correctly using sign extended addresses *OR* using sign extended addresses where we should use linear instead.

Regards,
Christian.

Am 17.01.19 um 09:04 schrieb Liu, Monk:
Hi Christian

I believe Wentao can fix the issue we it by below step:

  1.  Return Virtual_address_max (UMD use it) to HOLE_START – RESERVED_SIZE
  2.  [optional] Still Keep virtual_address_offset to RESERVED_SIZE (current way, I think it’s because previously we put CSA in 0 --> RESERVED_SIZE space)
  3.  Put CSA in HOLE_START – RESERVED_SIZE  ==> HOLE_START (it’s current design)

I don’t get where above scheme is not correct … can you give more explain for the GMC_HOLE_START ?

e.g.

  1.  why you set GMC_HOLE_START to 0x8’000’0000’0000 (half size of MAX of 48bit address space) ? is it for HSA purpose to make sure GPU address can also be used for CPU address ?
  2.  now MAX_PFN is 1’000’0000’0000, do you need to change GMC_HOLE_START ?

thanks
we need some catch up

/Monk

From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org><mailto:amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Koenig, Christian
Sent: Thursday, January 17, 2019 3:39 PM
To: Lou, Wentao <Wentao.Lou at amd.com><mailto:Wentao.Lou at amd.com>; Liu, Monk <Monk.Liu at amd.com><mailto:Monk.Liu at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>; Zhu, Rex <Rex.Zhu at amd.com><mailto:Rex.Zhu at amd.com>
Cc: Deng, Emily <Emily.Deng at amd.com><mailto:Emily.Deng at amd.com>
Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Am 17.01.19 um 04:17 schrieb Lou, Wentao:
Hi Christian,

Your solution as:
addr = (max_pfn - (AMDGPU_VA_RESERVED_SIZE >> AMDGPU_PAGE_SHIFT)) << AMDGPU_PAGE_SHIFT;
now max_pfn = 0x10 0000 0000, AMDGPU_VA_RESERVED_SIZE = 0x10 0000, AMDGPU_PAGE_SHIFT = 12
Still got addr = 0xFFFF FFF0 0000, which would cause ring gfx timeout.

But 0xFFFF FFF0 0000 is the correct address, if that is causing a problem then there is a bug somewhere else.

Please try to use AMDGPU_GMC_HOLE_START-AMDGPU_VA_RESERVED_SIZE as well. Does that work?

Before commit 1bf621c42137926ac249af761c0190a9258aa0db, vm_size was 32GB, and csa_addr was under AMDGPU_GMC_HOLE_START.

Wait a second why was the vm_size 32GB? This is on a Vega10 isn't it?

I didn’t understand why csa_addr need to be above AMDGPU_GMC_HOLE_START now.

On Vega10 the lower range, e.g. everything below AMDGPU_GMC_HOLE_START is reserved for SVA.

Regards,
Christian.

Thanks.

BR,
Wentao

From: Koenig, Christian <Christian.Koenig at amd.com><mailto:Christian.Koenig at amd.com>
Sent: Wednesday, January 16, 2019 5:48 PM
To: Lou, Wentao <Wentao.Lou at amd.com><mailto:Wentao.Lou at amd.com>; Liu, Monk <Monk.Liu at amd.com><mailto:Monk.Liu at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>; Zhu, Rex <Rex.Zhu at amd.com><mailto:Rex.Zhu at amd.com>
Cc: Deng, Emily <Emily.Deng at amd.com><mailto:Emily.Deng at amd.com>
Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Hi Wentao,

well the problem is you don't seem to understand how the hardware works.

See the engines see an MC address space with a hole in the middle, similar to the how x86 64bit CPU address space works. But the page tables are programmed linearly.

So the calculation in amdgpu_driver_open_kms() is correct because it takes the MC address and mages a linear page table index from it again.

The only thing we might need to fix here is shifting max_pfn before the subtraction and I doubt that even that is necessary.

Regards,
Christian.

Am 16.01.19 um 10:34 schrieb Lou, Wentao:

Hi Christian,

Now vm_size was set to 0x4 0000 GB by below commit:

1bf621c42137926ac249af761c0190a9258aa0db drm/amdgpu: Remove unnecessary VM size calculations

So that max_pfn would be 0x10 0000 0000.

amdgpu_csa_vaddr would make max_pfn << 12 to get 0x1 0000 0000 0000, and then minus AMDGPU_VA_RESERVED_SIZE, to get 0xFFFF FFF0 0000

unfortunately this number was between AMDGPU_GMC_HOLE_START and AMDGPU_GMC_HOLE_END, so that amdgpu_gmc_sign_extend was called to make it 0xFFFF FFFF FFF0 0000

in amdgpu_driver_open_kms, extended csa_addr cannot be passed into amdgpu_map_static_csa directly, it would be above the limit of max_pfn.

So that csa_addr was restricted by AMDGPU_GMC_HOLE_MASK to make it possible for amdgpu_vm_alloc_pts.

But this restriction by AMDGPU_GMC_HOLE_MASK would make the address fall back into AMDGPU_GMC_HOLE again,  which causing GPU reset.

We just put amdgpu_csa_vaddr back to AMDGPU_GMC_HOLE_START, to avoid the address touching AMDGPU_GMC_HOLE.

By the way, if max_pfn was shift much to the left, it would always get zero, with or without min(*,*).

BR,

Wentao

-----Original Message-----
From: Koenig, Christian <Christian.Koenig at amd.com><mailto:Christian.Koenig at amd.com>
Sent: Tuesday, January 15, 2019 4:02 PM
To: Liu, Monk <Monk.Liu at amd.com><mailto:Monk.Liu at amd.com>; Lou, Wentao <Wentao.Lou at amd.com><mailto:Wentao.Lou at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>; Zhu, Rex <Rex.Zhu at amd.com><mailto:Rex.Zhu at amd.com>
Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than AMDGPU_GMC_HOLE_START

Am 15.01.19 um 07:19 schrieb Liu, Monk:

> The max_pfn is now 1'0000'0000'0000'0000 (bytes) which is above 48 bit now, and it with AMDGPU_GMC_HOLE_MASK make it to zero ....

>

> And in code "amdgpu_driver_open_kms()" I saw @Zhu, Rex write the code as :

>

> "csa_addr = amdgpu_csa_vadr(adev) & AMDGPU_GMC_HOLE_MASK", I think this is wrong since you intentionally place the csa above GMC hole, right ?

The fix is just completely incorrect since min(adev->vm_manager.max_pfn << AMDGPU_GPU_PAGE_SHIFT, AMDGPU_GMC_HOLE_START) still gives you 0 when we shift max_pfn to much to the left.

The correct solution is to substract the reserved size first and then shift. E.g.:

addr = (max_pfn - (AMDGPU_VA_RESERVED_SIZE >> AMDGPU_PAGE_SHIFT)) << AMDGPU_PAGE_SHIFT;

Regards,

Christian.

>

> Looks like  we should modify this place

>

> /Monk

>

> -----Original Message-----

> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org<mailto:amd-gfx-bounces at lists.freedesktop.org>> On Behalf Of

> Christian K?nig

> Sent: Monday, January 14, 2019 9:05 PM

> To: Lou, Wentao <Wentao.Lou at amd.com<mailto:Wentao.Lou at amd.com>>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>

> Subject: Re: [PATCH] drm/amdgpu: csa_vaddr should not larger than

> AMDGPU_GMC_HOLE_START

>

> Am 14.01.19 um 09:40 schrieb wentalou:

>> After removing unnecessary VM size calculations, vm_manager.max_pfn

>> would reach 0x10,0000,0000 max_pfn << AMDGPU_GPU_PAGE_SHIFT exceeding

>> AMDGPU_GMC_HOLE_START would caused GPU reset.

>>

>> Change-Id: I47ad0be2b0bd9fb7490c4e1d7bb7bdacf71132cb

>> Signed-off-by: wentalou <Wentao.Lou at amd.com<mailto:Wentao.Lou at amd.com>>

> NAK, that is incorrect. We intentionally place the csa above the GMC hole.

>

> Regards,

> Christian.

>

>> ---

>>    drivers/gpu/drm/amd/amdgpu/amdgpu_csa.c | 3 ++-

>>    1 file changed, 2 insertions(+), 1 deletion(-)

>>

>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_csa.c

>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_csa.c

>> index 7e22be7..dd3bd01 100644

>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_csa.c

>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_csa.c

>> @@ -26,7 +26,8 @@

>>

>>    uint64_t amdgpu_csa_vaddr(struct amdgpu_device *adev)

>>    {

>> -        uint64_t addr = adev->vm_manager.max_pfn << AMDGPU_GPU_PAGE_SHIFT;

>> +       uint64_t addr = min(adev->vm_manager.max_pfn << AMDGPU_GPU_PAGE_SHIFT,

>> +                                                    AMDGPU_GMC_HOLE_START);

>>

>>          addr -= AMDGPU_VA_RESERVED_SIZE;

>>          addr = amdgpu_gmc_sign_extend(addr);

> _______________________________________________

> amd-gfx mailing list

> amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>

> https://lists.freedesktop.org/mailman/listinfo/amd-gfx

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