FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

[gregkh]

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052750-fondness-revocable-a23b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7170130e4c72ce0caa0cb42a1627c635cc262821 Mon Sep 17 00:00:00 2001
From: Balbir Singh <balbirs@nvidia.com>
Date: Tue, 1 Apr 2025 11:07:52 +1100
Subject: [PATCH] x86/mm/init: Handle the special case of device private pages
 in add_pages(), to not increase max_pfn and trigger dma_addressing_limited()
 bounce buffers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

As Bert Karwatzki reported, the following recent commit causes a
performance regression on AMD iGPU and dGPU systems:

  7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems")

It exposed a bug with nokaslr and zone device interaction.

The root cause of the bug is that, the GPU driver registers a zone
device private memory region. When KASLR is disabled or the above commit
is applied, the direct_map_physmem_end is set to much higher than 10 TiB
typically to the 64TiB address. When zone device private memory is added
to the system via add_pages(), it bumps up the max_pfn to the same
value. This causes dma_addressing_limited() to return true, since the
device cannot address memory all the way up to max_pfn.

This caused a regression for games played on the iGPU, as it resulted in
the DMA32 zone being used for GPU allocations.

Fix this by not bumping up max_pfn on x86 systems, when pgmap is passed
into add_pages(). The presence of pgmap is used to determine if device
private memory is being added via add_pages().

More details:

devm_request_mem_region() and request_free_mem_region() request for
device private memory. iomem_resource is passed as the base resource
with start and end parameters. iomem_resource's end depends on several
factors, including the platform and virtualization. On x86 for example
on bare metal, this value is set to boot_cpu_data.x86_phys_bits.
boot_cpu_data.x86_phys_bits can change depending on support for MKTME.
By default it is set to the same as log2(direct_map_physmem_end) which
is 46 to 52 bits depending on the number of levels in the page table.
The allocation routines used iomem_resource's end and
direct_map_physmem_end to figure out where to allocate the region.

[ arch/powerpc is also impacted by this problem, but this patch does not fix
  the issue for PowerPC. ]

Testing:

 1. Tested on a virtual machine with test_hmm for zone device inseration

 2. A previous version of this patch was tested by Bert, please see:
    https://lore.kernel.org/lkml/d87680bab997fdc9fb4e638983132af235d9a03a.camel@web.de/

[ mingo: Clarified the comments and the changelog. ]

Reported-by: Bert Karwatzki <spasswolf@web.de>
Tested-by: Bert Karwatzki <spasswolf@web.de>
Fixes: 7ffb791423c7 ("x86/kaslr: Reduce KASLR entropy on most x86 systems")
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Link: https://lore.kernel.org/r/20250401000752.249348-1-balbirs@nvidia.com

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 519aa53114fa..821a0b53b21c 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -959,9 +959,18 @@ int add_pages(int nid, unsigned long start_pfn, unsigned long nr_pages,
 	ret = __add_pages(nid, start_pfn, nr_pages, params);
 	WARN_ON_ONCE(ret);
 
-	/* update max_pfn, max_low_pfn and high_memory */
-	update_end_of_memory_vars(start_pfn << PAGE_SHIFT,
-				  nr_pages << PAGE_SHIFT);
+	/*
+	 * Special case: add_pages() is called by memremap_pages() for adding device
+	 * private pages. Do not bump up max_pfn in the device private path,
+	 * because max_pfn changes affect dma_addressing_limited().
+	 *
+	 * dma_addressing_limited() returning true when max_pfn is the device's
+	 * addressable memory can force device drivers to use bounce buffers
+	 * and impact their performance negatively:
+	 */
+	if (!params->pgmap)
+		/* update max_pfn, max_low_pfn and high_memory */
+		update_end_of_memory_vars(start_pfn << PAGE_SHIFT, nr_pages << PAGE_SHIFT);
 
 	return ret;
 }

Re: FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

[Balbir Singh]

On 5/28/25 02:55, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 5.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> git checkout FETCH_HEAD
> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052750-fondness-revocable-a23b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
> 
> Possible dependencies:
> 
> 

We only need it if 7ffb791423c7 gets backported. I can take a look and see if we need the patch and why the application of the patch failed

Balbir

Re: FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

[Balbir Singh]

On 5/28/25 08:59, Balbir Singh wrote:
> On 5/28/25 02:55, gregkh@linuxfoundation.org wrote:
>>
>> The patch below does not apply to the 5.15-stable tree.
>> If someone wants it applied there, or to any other stable or longterm
>> tree, then please email the backport, including the original git commit
>> id to <stable@vger.kernel.org>.
>>
>> To reproduce the conflict and resubmit, you may use the following commands:
>>
>> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
>> git checkout FETCH_HEAD
>> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
>> # <resolve conflicts, build, test, etc.>
>> git commit -s
>> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052750-fondness-revocable-a23b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
>>
>> Possible dependencies:
>>
>>
> 
> We only need it if 7ffb791423c7 gets backported. I can take a look and see if we need the patch and why the application of the patch failed
> 
> Balbir
> 

Hi, Greg

FYI: I was able to cherry pick 7170130e4c72ce0caa0cb42a1627c635cc262821 on top of
5.15.y (5.15.184) on my machine

I ran the steps below

>> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
>> git checkout FETCH_HEAD
>> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821

I saw no conflicts. Am I missing something?

Balbir

Re: FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

[Greg KH]

On Fri, May 30, 2025 at 07:54:32PM +1000, Balbir Singh wrote:
> On 5/28/25 08:59, Balbir Singh wrote:
> > On 5/28/25 02:55, gregkh@linuxfoundation.org wrote:
> >>
> >> The patch below does not apply to the 5.15-stable tree.
> >> If someone wants it applied there, or to any other stable or longterm
> >> tree, then please email the backport, including the original git commit
> >> id to <stable@vger.kernel.org>.
> >>
> >> To reproduce the conflict and resubmit, you may use the following commands:
> >>
> >> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> >> git checkout FETCH_HEAD
> >> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
> >> # <resolve conflicts, build, test, etc.>
> >> git commit -s
> >> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052750-fondness-revocable-a23b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
> >>
> >> Possible dependencies:
> >>
> >>
> > 
> > We only need it if 7ffb791423c7 gets backported. I can take a look and see if we need the patch and why the application of the patch failed
> > 
> > Balbir
> > 
> 
> Hi, Greg
> 
> FYI: I was able to cherry pick 7170130e4c72ce0caa0cb42a1627c635cc262821 on top of
> 5.15.y (5.15.184) on my machine
> 
> I ran the steps below
> 
> >> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> >> git checkout FETCH_HEAD
> >> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
> 
> I saw no conflicts. Am I missing something?

Did you test build it as the instructions above asked you to do?

Try it and see what happens :)

thanks,

greg k-h

Re: FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

[Balbir Singh]

On 5/30/25 21:59, Greg KH wrote:
> On Fri, May 30, 2025 at 07:54:32PM +1000, Balbir Singh wrote:
>> On 5/28/25 08:59, Balbir Singh wrote:
>>> On 5/28/25 02:55, gregkh@linuxfoundation.org wrote:
>>>>
>>>> The patch below does not apply to the 5.15-stable tree.
>>>> If someone wants it applied there, or to any other stable or longterm
>>>> tree, then please email the backport, including the original git commit
>>>> id to <stable@vger.kernel.org>.
>>>>
>>>> To reproduce the conflict and resubmit, you may use the following commands:
>>>>
>>>> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
>>>> git checkout FETCH_HEAD
>>>> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
>>>> # <resolve conflicts, build, test, etc.>
>>>> git commit -s
>>>> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052750-fondness-revocable-a23b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
>>>>
>>>> Possible dependencies:
>>>>
>>>>
>>>
>>> We only need it if 7ffb791423c7 gets backported. I can take a look and see if we need the patch and why the application of the patch failed
>>>
>>> Balbir
>>>
>>
>> Hi, Greg
>>
>> FYI: I was able to cherry pick 7170130e4c72ce0caa0cb42a1627c635cc262821 on top of
>> 5.15.y (5.15.184) on my machine
>>
>> I ran the steps below
>>
>>>> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
>>>> git checkout FETCH_HEAD
>>>> git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
>>
>> I saw no conflicts. Am I missing something?
> 
> Did you test build it as the instructions above asked you to do?
> 
> Try it and see what happens :)

I stopped after cherry-pick, I thought the patch failed to apply as in cherry-pick failed :)
So I did not try and build it. 

Balbir Singh

Re: FAILED: patch "[PATCH] x86/mm/init: Handle the special case of device private pages" failed to apply to 5.15-stable tree

[Bert Karwatzki]

Am Freitag, dem 30.05.2025 um 22:08 +1000 schrieb Balbir Singh:
> On 5/30/25 21:59, Greg KH wrote:
> > On Fri, May 30, 2025 at 07:54:32PM +1000, Balbir Singh wrote:
> > > On 5/28/25 08:59, Balbir Singh wrote:
> > > > On 5/28/25 02:55, gregkh@linuxfoundation.org wrote:
> > > > > 
> > > > > The patch below does not apply to the 5.15-stable tree.
> > > > > If someone wants it applied there, or to any other stable or longterm
> > > > > tree, then please email the backport, including the original git commit
> > > > > id to <stable@vger.kernel.org>.
> > > > > 
> > > > > To reproduce the conflict and resubmit, you may use the following commands:
> > > > > 
> > > > > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> > > > > git checkout FETCH_HEAD
> > > > > git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
> > > > > # <resolve conflicts, build, test, etc.>
> > > > > git commit -s
> > > > > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025052750-fondness-revocable-a23b@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
> > > > > 
> > > > > Possible dependencies:
> > > > > 
> > > > > 
> > > > 
> > > > We only need it if 7ffb791423c7 gets backported. I can take a look and see if we need the patch and why the application of the patch failed
> > > > 
> > > > Balbir
> > > > 
> > > 
> > > Hi, Greg
> > > 
> > > FYI: I was able to cherry pick 7170130e4c72ce0caa0cb42a1627c635cc262821 on top of
> > > 5.15.y (5.15.184) on my machine
> > > 
> > > I ran the steps below
> > > 
> > > > > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> > > > > git checkout FETCH_HEAD
> > > > > git cherry-pick -x 7170130e4c72ce0caa0cb42a1627c635cc262821
> > > 
> > > I saw no conflicts. Am I missing something?
> > 
> > Did you test build it as the instructions above asked you to do?
> > 
> > Try it and see what happens :)
> 
> I stopped after cherry-pick, I thought the patch failed to apply as in cherry-pick failed :)
> So I did not try and build it. 
> 
> Balbir Singh

The member pagemap in struct mhp_params was introduced in v5.19-rc1 so the build fails
for v5.15.*.

Bert Karwatzki