Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
WARN_ON_ONCE and returning an error. This is to ensure users of the
vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
and get an indication of an error without panicing the kernel.
This will help identifying drivers that need to clear VM_PFNMAP before
using dmabuf system heap which is moving to use vm_insert_page.
Suggested-by: Christoph Hellwig <[email protected]>
Signed-off-by: Suren Baghdasaryan <[email protected]>
---
mm/memory.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index feff48e1465a..e503c9801cd9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
return -EINVAL;
if (!(vma->vm_flags & VM_MIXEDMAP)) {
BUG_ON(mmap_read_trylock(vma->vm_mm));
- BUG_ON(vma->vm_flags & VM_PFNMAP);
+ if (WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP))
+ return -EINVAL;
vma->vm_flags |= VM_MIXEDMAP;
}
return insert_page(vma, addr, page, vma->vm_page_prot);
--
2.30.0.365.g02bc693789-goog
Currently system heap maps its buffers with VM_PFNMAP flag using
remap_pfn_range. This results in such buffers not being accounted
for in PSS calculations because vm treats this memory as having no
page structs. Without page structs there are no counters representing
how many processes are mapping a page and therefore PSS calculation
is impossible.
Historically, ION driver used to map its buffers as VM_PFNMAP areas
due to memory carveouts that did not have page structs [1]. That
is not the case anymore and it seems there was desire to move away
from remap_pfn_range [2].
Dmabuf system heap design inherits this ION behavior and maps its
pages using remap_pfn_range even though allocated pages are backed
by page structs.
Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
in [1]. This would allow correct PSS calculation for dmabufs.
[1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
[2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
(sorry, could not find lore links for these discussions)
Suggested-by: Laura Abbott <[email protected]>
Signed-off-by: Suren Baghdasaryan <[email protected]>
---
v1 posted at: https://lore.kernel.org/patchwork/patch/1372409/
changes in v2:
- removed VM_PFNMAP clearing part of the patch, per Minchan and Christoph
- created prerequisite patch to replace BUG_ON with WARN_ON_ONCE, per Christoph
drivers/dma-buf/heaps/system_heap.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 17e0e9a68baf..4983f18cc2ce 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -203,8 +203,7 @@ static int system_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
for_each_sgtable_page(table, &piter, vma->vm_pgoff) {
struct page *page = sg_page_iter_page(&piter);
- ret = remap_pfn_range(vma, addr, page_to_pfn(page), PAGE_SIZE,
- vma->vm_page_prot);
+ ret = vm_insert_page(vma, addr, page);
if (ret)
return ret;
addr += PAGE_SIZE;
--
2.30.0.365.g02bc693789-goog
Hi:
On 2021/2/3 8:31, Suren Baghdasaryan wrote:
> Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> WARN_ON_ONCE and returning an error. This is to ensure users of the
> vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> and get an indication of an error without panicing the kernel.
> This will help identifying drivers that need to clear VM_PFNMAP before
> using dmabuf system heap which is moving to use vm_insert_page.
>
> Suggested-by: Christoph Hellwig <[email protected]>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
Looks reasonable. Thanks.
Reviewed-by: Miaohe Lin <[email protected]>
> ---
> mm/memory.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index feff48e1465a..e503c9801cd9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
> return -EINVAL;
> if (!(vma->vm_flags & VM_MIXEDMAP)) {
> BUG_ON(mmap_read_trylock(vma->vm_mm));
> - BUG_ON(vma->vm_flags & VM_PFNMAP);
> + if (WARN_ON_ONCE(vma->vm_flags & VM_PFNMAP))
> + return -EINVAL;
> vma->vm_flags |= VM_MIXEDMAP;
> }
> return insert_page(vma, addr, page, vma->vm_page_prot);
>
On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> WARN_ON_ONCE and returning an error. This is to ensure users of the
> vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> and get an indication of an error without panicing the kernel.
> This will help identifying drivers that need to clear VM_PFNMAP before
> using dmabuf system heap which is moving to use vm_insert_page.
>
> Suggested-by: Christoph Hellwig <[email protected]>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
> ---
> mm/memory.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index feff48e1465a..e503c9801cd9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
> return -EINVAL;
> if (!(vma->vm_flags & VM_MIXEDMAP)) {
> BUG_ON(mmap_read_trylock(vma->vm_mm));
Better to replace above BUG_ON with WARN_ON_ONCE, too?
On Tue, Feb 02, 2021 at 04:31:34PM -0800, Suren Baghdasaryan wrote:
> Currently system heap maps its buffers with VM_PFNMAP flag using
> remap_pfn_range. This results in such buffers not being accounted
> for in PSS calculations because vm treats this memory as having no
> page structs. Without page structs there are no counters representing
> how many processes are mapping a page and therefore PSS calculation
> is impossible.
> Historically, ION driver used to map its buffers as VM_PFNMAP areas
> due to memory carveouts that did not have page structs [1]. That
> is not the case anymore and it seems there was desire to move away
> from remap_pfn_range [2].
> Dmabuf system heap design inherits this ION behavior and maps its
> pages using remap_pfn_range even though allocated pages are backed
> by page structs.
> Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
> in [1]. This would allow correct PSS calculation for dmabufs.
>
> [1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
> [2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
> (sorry, could not find lore links for these discussions)
>
> Suggested-by: Laura Abbott <[email protected]>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
Reviewed-by: Minchan Kim <[email protected]>
A note: This patch makes dmabuf system heap accounted as PSS so
if someone has relies on the size, they will see the bloat.
IIRC, there was some debate whether PSS accounting for their
buffer is correct or not. If it'd be a problem, we need to
discuss how to solve it(maybe, vma->vm_flags and reintroduce
remap_pfn_range for them to be respected).
On Tue, Feb 2, 2021 at 5:31 PM Minchan Kim <[email protected]> wrote:
>
> On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> > Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> > WARN_ON_ONCE and returning an error. This is to ensure users of the
> > vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> > and get an indication of an error without panicing the kernel.
> > This will help identifying drivers that need to clear VM_PFNMAP before
> > using dmabuf system heap which is moving to use vm_insert_page.
> >
> > Suggested-by: Christoph Hellwig <[email protected]>
> > Signed-off-by: Suren Baghdasaryan <[email protected]>
> > ---
> > mm/memory.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/mm/memory.c b/mm/memory.c
> > index feff48e1465a..e503c9801cd9 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -1827,7 +1827,8 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
> > return -EINVAL;
> > if (!(vma->vm_flags & VM_MIXEDMAP)) {
> > BUG_ON(mmap_read_trylock(vma->vm_mm));
>
> Better to replace above BUG_ON with WARN_ON_ONCE, too?
If nobody objects I'll do that in the next respin. Thanks!
>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
>
On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> WARN_ON_ONCE and returning an error. This is to ensure users of the
> vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> and get an indication of an error without panicing the kernel.
> This will help identifying drivers that need to clear VM_PFNMAP before
> using dmabuf system heap which is moving to use vm_insert_page.
NACK.
The system may not _panic_, but it is clearly now _broken_. The device
doesn't work, and so the system is useless. You haven't really improved
anything here. Just bloated the kernel with yet another _ONCE variable
that in a normal system will never ever ever be triggered.
On Tue, Feb 2, 2021 at 5:39 PM Minchan Kim <[email protected]> wrote:
>
> On Tue, Feb 02, 2021 at 04:31:34PM -0800, Suren Baghdasaryan wrote:
> > Currently system heap maps its buffers with VM_PFNMAP flag using
> > remap_pfn_range. This results in such buffers not being accounted
> > for in PSS calculations because vm treats this memory as having no
> > page structs. Without page structs there are no counters representing
> > how many processes are mapping a page and therefore PSS calculation
> > is impossible.
> > Historically, ION driver used to map its buffers as VM_PFNMAP areas
> > due to memory carveouts that did not have page structs [1]. That
> > is not the case anymore and it seems there was desire to move away
> > from remap_pfn_range [2].
> > Dmabuf system heap design inherits this ION behavior and maps its
> > pages using remap_pfn_range even though allocated pages are backed
> > by page structs.
> > Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
> > in [1]. This would allow correct PSS calculation for dmabufs.
> >
> > [1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
> > [2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
> > (sorry, could not find lore links for these discussions)
> >
> > Suggested-by: Laura Abbott <[email protected]>
> > Signed-off-by: Suren Baghdasaryan <[email protected]>
> Reviewed-by: Minchan Kim <[email protected]>
>
> A note: This patch makes dmabuf system heap accounted as PSS so
> if someone has relies on the size, they will see the bloat.
> IIRC, there was some debate whether PSS accounting for their
> buffer is correct or not. If it'd be a problem, we need to
> discuss how to solve it(maybe, vma->vm_flags and reintroduce
> remap_pfn_range for them to be respected).
I did not see debates about not including *mapped* dmabufs into PSS
calculation. I remember people were discussing how to account dmabufs
referred only by the FD but that is a different discussion. If the
buffer is mapped into the address space of a process then IMHO
including it into PSS of that process is not controversial.
On Tue, Feb 2, 2021 at 4:31 PM Suren Baghdasaryan <[email protected]> wrote:
> Currently system heap maps its buffers with VM_PFNMAP flag using
> remap_pfn_range. This results in such buffers not being accounted
> for in PSS calculations because vm treats this memory as having no
> page structs. Without page structs there are no counters representing
> how many processes are mapping a page and therefore PSS calculation
> is impossible.
> Historically, ION driver used to map its buffers as VM_PFNMAP areas
> due to memory carveouts that did not have page structs [1]. That
> is not the case anymore and it seems there was desire to move away
> from remap_pfn_range [2].
> Dmabuf system heap design inherits this ION behavior and maps its
> pages using remap_pfn_range even though allocated pages are backed
> by page structs.
> Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
> in [1]. This would allow correct PSS calculation for dmabufs.
>
> [1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
> [2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
> (sorry, could not find lore links for these discussions)
>
> Suggested-by: Laura Abbott <[email protected]>
> Signed-off-by: Suren Baghdasaryan <[email protected]>
For consistency, do we need something similar for the cma heap as well?
thanks
-john
On Tue, Feb 2, 2021 at 6:07 PM John Stultz <[email protected]> wrote:
>
> On Tue, Feb 2, 2021 at 4:31 PM Suren Baghdasaryan <[email protected]> wrote:
> > Currently system heap maps its buffers with VM_PFNMAP flag using
> > remap_pfn_range. This results in such buffers not being accounted
> > for in PSS calculations because vm treats this memory as having no
> > page structs. Without page structs there are no counters representing
> > how many processes are mapping a page and therefore PSS calculation
> > is impossible.
> > Historically, ION driver used to map its buffers as VM_PFNMAP areas
> > due to memory carveouts that did not have page structs [1]. That
> > is not the case anymore and it seems there was desire to move away
> > from remap_pfn_range [2].
> > Dmabuf system heap design inherits this ION behavior and maps its
> > pages using remap_pfn_range even though allocated pages are backed
> > by page structs.
> > Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
> > in [1]. This would allow correct PSS calculation for dmabufs.
> >
> > [1] https://driverdev-devel.linuxdriverproject.narkive.com/v0fJGpaD/using-ion-memory-for-direct-io
> > [2] http://driverdev.linuxdriverproject.org/pipermail/driverdev-devel/2018-October/127519.html
> > (sorry, could not find lore links for these discussions)
> >
> > Suggested-by: Laura Abbott <[email protected]>
> > Signed-off-by: Suren Baghdasaryan <[email protected]>
>
> For consistency, do we need something similar for the cma heap as well?
Good question. Let me look closer into it.
>
> thanks
> -john
On Tue, Feb 2, 2021 at 5:55 PM Matthew Wilcox <[email protected]> wrote:
>
> On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> > Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> > WARN_ON_ONCE and returning an error. This is to ensure users of the
> > vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> > and get an indication of an error without panicing the kernel.
> > This will help identifying drivers that need to clear VM_PFNMAP before
> > using dmabuf system heap which is moving to use vm_insert_page.
>
> NACK.
>
> The system may not _panic_, but it is clearly now _broken_. The device
> doesn't work, and so the system is useless. You haven't really improved
> anything here. Just bloated the kernel with yet another _ONCE variable
> that in a normal system will never ever ever be triggered.
We had a discussion in https://lore.kernel.org/patchwork/patch/1372409
about how some DRM drivers set up their VMAs with VM_PFNMAP before
mapping them. We want to use vm_insert_page instead of remap_pfn_range
in the dmabuf heaps so that this memory is visible in PSS. However if
a driver that sets VM_PFNMAP tries to use a dmabuf heap, it will step
into this BUG_ON. We wanted to catch and gradually fix such drivers
but without causing a panic in the process. I hope this clarifies the
reasons why I'm making this change and I'm open to other ideas if they
would address this issue in a better way.
Am 03.02.21 um 03:02 schrieb Suren Baghdasaryan:
> On Tue, Feb 2, 2021 at 5:39 PM Minchan Kim <[email protected]> wrote:
>> On Tue, Feb 02, 2021 at 04:31:34PM -0800, Suren Baghdasaryan wrote:
>>> Currently system heap maps its buffers with VM_PFNMAP flag using
>>> remap_pfn_range. This results in such buffers not being accounted
>>> for in PSS calculations because vm treats this memory as having no
>>> page structs. Without page structs there are no counters representing
>>> how many processes are mapping a page and therefore PSS calculation
>>> is impossible.
>>> Historically, ION driver used to map its buffers as VM_PFNMAP areas
>>> due to memory carveouts that did not have page structs [1]. That
>>> is not the case anymore and it seems there was desire to move away
>>> from remap_pfn_range [2].
>>> Dmabuf system heap design inherits this ION behavior and maps its
>>> pages using remap_pfn_range even though allocated pages are backed
>>> by page structs.
>>> Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
>>> in [1]. This would allow correct PSS calculation for dmabufs.
>>>
>>> [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdriverdev-devel.linuxdriverproject.narkive.com%2Fv0fJGpaD%2Fusing-ion-memory-for-direct-io&data=04%7C01%7Cchristian.koenig%40amd.com%7Cb4c145b86dd0472c943c08d8c7e7ba4b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479145389160353%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=W1N%2B%2BlcFDaRSvXdSPe5hPNMRByHfGkU7Uc3cmM3FCTU%3D&reserved=0
>>> [2] https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdriverdev.linuxdriverproject.org%2Fpipermail%2Fdriverdev-devel%2F2018-October%2F127519.html&data=04%7C01%7Cchristian.koenig%40amd.com%7Cb4c145b86dd0472c943c08d8c7e7ba4b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479145389160353%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=jQxSzKEr52lUcAIx%2FuBHMJ7yOgof%2FVMlW9%2BB2f%2FoS%2FE%3D&reserved=0
>>> (sorry, could not find lore links for these discussions)
>>>
>>> Suggested-by: Laura Abbott <[email protected]>
>>> Signed-off-by: Suren Baghdasaryan <[email protected]>
>> Reviewed-by: Minchan Kim <[email protected]>
>>
>> A note: This patch makes dmabuf system heap accounted as PSS so
>> if someone has relies on the size, they will see the bloat.
>> IIRC, there was some debate whether PSS accounting for their
>> buffer is correct or not. If it'd be a problem, we need to
>> discuss how to solve it(maybe, vma->vm_flags and reintroduce
>> remap_pfn_range for them to be respected).
> I did not see debates about not including *mapped* dmabufs into PSS
> calculation. I remember people were discussing how to account dmabufs
> referred only by the FD but that is a different discussion. If the
> buffer is mapped into the address space of a process then IMHO
> including it into PSS of that process is not controversial.
Well, I think it is. And to be honest this doesn't looks like a good
idea to me since it will eventually lead to double accounting of system
heap DMA-bufs.
As discussed multiple times it is illegal to use the struct page of a
DMA-buf. This case here is a bit special since it is the owner of the
pages which does that, but I'm not sure if this won't cause problems
elsewhere as well.
A more appropriate solution would be to held processes accountable for
resources they have allocated through device drivers.
Regards,
Christian.
On Wed, Feb 3, 2021 at 2:57 AM Matthew Wilcox <[email protected]> wrote:
>
> On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> > Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> > WARN_ON_ONCE and returning an error. This is to ensure users of the
> > vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> > and get an indication of an error without panicing the kernel.
> > This will help identifying drivers that need to clear VM_PFNMAP before
> > using dmabuf system heap which is moving to use vm_insert_page.
>
> NACK.
>
> The system may not _panic_, but it is clearly now _broken_. The device
> doesn't work, and so the system is useless. You haven't really improved
> anything here. Just bloated the kernel with yet another _ONCE variable
> that in a normal system will never ever ever be triggered.
Also, what the heck are you doing with your drivers? dma-buf mmap must
call dma_buf_mmap(), even for forwarded/redirected mmaps from driver
char nodes. If that doesn't work we have some issues with the calling
contract for that function, not in vm_insert_page.
Finally why exactly do we need to make this switch for system heap?
I've recently looked at gup usage by random drivers, and found a lot
of worrying things there. gup on dma-buf is really bad idea in
general.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
On Wed, Feb 3, 2021 at 12:06 AM Christian König
<[email protected]> wrote:
>
> Am 03.02.21 um 03:02 schrieb Suren Baghdasaryan:
> > On Tue, Feb 2, 2021 at 5:39 PM Minchan Kim <[email protected]> wrote:
> >> On Tue, Feb 02, 2021 at 04:31:34PM -0800, Suren Baghdasaryan wrote:
> >>> Currently system heap maps its buffers with VM_PFNMAP flag using
> >>> remap_pfn_range. This results in such buffers not being accounted
> >>> for in PSS calculations because vm treats this memory as having no
> >>> page structs. Without page structs there are no counters representing
> >>> how many processes are mapping a page and therefore PSS calculation
> >>> is impossible.
> >>> Historically, ION driver used to map its buffers as VM_PFNMAP areas
> >>> due to memory carveouts that did not have page structs [1]. That
> >>> is not the case anymore and it seems there was desire to move away
> >>> from remap_pfn_range [2].
> >>> Dmabuf system heap design inherits this ION behavior and maps its
> >>> pages using remap_pfn_range even though allocated pages are backed
> >>> by page structs.
> >>> Replace remap_pfn_range with vm_insert_page, following Laura's suggestion
> >>> in [1]. This would allow correct PSS calculation for dmabufs.
> >>>
> >>> [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdriverdev-devel.linuxdriverproject.narkive.com%2Fv0fJGpaD%2Fusing-ion-memory-for-direct-io&data=04%7C01%7Cchristian.koenig%40amd.com%7Cb4c145b86dd0472c943c08d8c7e7ba4b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479145389160353%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=W1N%2B%2BlcFDaRSvXdSPe5hPNMRByHfGkU7Uc3cmM3FCTU%3D&reserved=0
> >>> [2] https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdriverdev.linuxdriverproject.org%2Fpipermail%2Fdriverdev-devel%2F2018-October%2F127519.html&data=04%7C01%7Cchristian.koenig%40amd.com%7Cb4c145b86dd0472c943c08d8c7e7ba4b%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637479145389160353%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=jQxSzKEr52lUcAIx%2FuBHMJ7yOgof%2FVMlW9%2BB2f%2FoS%2FE%3D&reserved=0
> >>> (sorry, could not find lore links for these discussions)
> >>>
> >>> Suggested-by: Laura Abbott <[email protected]>
> >>> Signed-off-by: Suren Baghdasaryan <[email protected]>
> >> Reviewed-by: Minchan Kim <[email protected]>
> >>
> >> A note: This patch makes dmabuf system heap accounted as PSS so
> >> if someone has relies on the size, they will see the bloat.
> >> IIRC, there was some debate whether PSS accounting for their
> >> buffer is correct or not. If it'd be a problem, we need to
> >> discuss how to solve it(maybe, vma->vm_flags and reintroduce
> >> remap_pfn_range for them to be respected).
> > I did not see debates about not including *mapped* dmabufs into PSS
> > calculation. I remember people were discussing how to account dmabufs
> > referred only by the FD but that is a different discussion. If the
> > buffer is mapped into the address space of a process then IMHO
> > including it into PSS of that process is not controversial.
>
> Well, I think it is. And to be honest this doesn't looks like a good
> idea to me since it will eventually lead to double accounting of system
> heap DMA-bufs.
Thanks for the comment! Could you please expand on this double
accounting issue? Do you mean userspace could double account dmabufs
because it expects dmabufs not to be part of PSS or is there some
in-kernel accounting mechanism that would be broken by this?
>
> As discussed multiple times it is illegal to use the struct page of a
> DMA-buf. This case here is a bit special since it is the owner of the
> pages which does that, but I'm not sure if this won't cause problems
> elsewhere as well.
I would be happy to keep things as they are but calculating dmabuf
contribution to PSS without struct pages is extremely inefficient and
becomes a real pain when we consider the possibilities of partial
mappings, when not the entire dmabuf is being mapped.
Calculating this would require parsing /proc/pid/maps for the process,
finding dmabuf mappings and the size for each one, then parsing
/proc/pid/maps for ALL processes in the system to see if the same
dmabufs are used by other processes and only then calculating the PSS.
I hope that explains the desire to use already existing struct pages
to obtain PSS in a much more efficient way.
>
> A more appropriate solution would be to held processes accountable for
> resources they have allocated through device drivers.
Are you suggesting some new kernel mechanism to account resources
allocated by a process via a driver? If so, any details?
>
> Regards,
> Christian.
>
> --
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
>
On Wed, Feb 3, 2021 at 12:52 AM Daniel Vetter <[email protected]> wrote:
>
> On Wed, Feb 3, 2021 at 2:57 AM Matthew Wilcox <[email protected]> wrote:
> >
> > On Tue, Feb 02, 2021 at 04:31:33PM -0800, Suren Baghdasaryan wrote:
> > > Replace BUG_ON(vma->vm_flags & VM_PFNMAP) in vm_insert_page with
> > > WARN_ON_ONCE and returning an error. This is to ensure users of the
> > > vm_insert_page that set VM_PFNMAP are notified of the wrong flag usage
> > > and get an indication of an error without panicing the kernel.
> > > This will help identifying drivers that need to clear VM_PFNMAP before
> > > using dmabuf system heap which is moving to use vm_insert_page.
> >
> > NACK.
> >
> > The system may not _panic_, but it is clearly now _broken_. The device
> > doesn't work, and so the system is useless. You haven't really improved
> > anything here. Just bloated the kernel with yet another _ONCE variable
> > that in a normal system will never ever ever be triggered.
>
> Also, what the heck are you doing with your drivers? dma-buf mmap must
> call dma_buf_mmap(), even for forwarded/redirected mmaps from driver
> char nodes. If that doesn't work we have some issues with the calling
> contract for that function, not in vm_insert_page.
The particular issue I observed (details were posted in
https://lore.kernel.org/patchwork/patch/1372409) is that DRM drivers
set VM_PFNMAP flag (via a call to drm_gem_mmap_obj) before calling
dma_buf_mmap. Some drivers clear that flag but some don't. I could not
find the answer to why VM_PFNMAP is required for dmabuf mappings and
maybe someone can explain that here?
If there is a reason to set this flag other than historical use of
carveout memory then we wanted to catch such cases and fix the drivers
that moved to using dmabuf heaps. However maybe there are other
reasons and if so I would be very grateful if someone could explain
them. That would help me to come up with a better solution.
> Finally why exactly do we need to make this switch for system heap?
> I've recently looked at gup usage by random drivers, and found a lot
> of worrying things there. gup on dma-buf is really bad idea in
> general.
The reason for the switch is to be able to account dmabufs allocated
using dmabuf heaps to the processes that map them. The next patch in
this series https://lore.kernel.org/patchwork/patch/1374851
implementing the switch contains more details and there is an active
discussion there. Would you mind joining that discussion to keep it in
one place?
Thanks!
> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
Am 03.02.21 um 21:20 schrieb Suren Baghdasaryan:
> [SNIP]
> If there is a reason to set this flag other than historical use of
> carveout memory then we wanted to catch such cases and fix the drivers
> that moved to using dmabuf heaps. However maybe there are other
> reasons and if so I would be very grateful if someone could explain
> them. That would help me to come up with a better solution.
Well one major reason for this is to prevent accounting of DMA-buf pages.
So you are going in circles here and trying to circumvent an intentional
behavior.
Daniel is right that this is the completely wrong approach and we need
to take a step back and think about it on a higher level.
Going to replay to his mail as well.
Regards,
Christian.