On 12/2/25 12:20, Jordan Niethe wrote:
> Hi,
>
> On 29/11/25 05:36, Matthew Brost wrote:
>> On Fri, Nov 28, 2025 at 03:41:41PM +1100, Jordan Niethe wrote:
>>> A future change will remove device private pages from the physical
>>> address space. This will mean that device private pages no longer have
>>> normal PFN and must be handled separately.
>>>
>>> Prepare for this by adding a HMM_PFN_DEVICE_PRIVATE flag to indicate
>>> that a hmm_pfn contains a PFN for a device private page.
>>>
>>> Signed-off-by: Jordan Niethe <[email protected]>
>>> Signed-off-by: Alistair Popple <[email protected]>
>>> ---
>>> include/linux/hmm.h | 2 ++
>>> mm/hmm.c | 2 +-
>>> 2 files changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
>>> index db75ffc949a7..df571fa75a44 100644
>>> --- a/include/linux/hmm.h
>>> +++ b/include/linux/hmm.h
>>> @@ -23,6 +23,7 @@ struct mmu_interval_notifier;
>>> * HMM_PFN_WRITE - if the page memory can be written to (requires
>>> HMM_PFN_VALID)
>>> * HMM_PFN_ERROR - accessing the pfn is impossible and the device should
>>> * fail. ie poisoned memory, special pages, no vma, etc
>>> + * HMM_PFN_DEVICE_PRIVATE - the pfn field contains a DEVICE_PRIVATE pfn.
>>> * HMM_PFN_P2PDMA - P2P page
>>> * HMM_PFN_P2PDMA_BUS - Bus mapped P2P transfer
>>> * HMM_PFN_DMA_MAPPED - Flag preserved on input-to-output transformation
>>> @@ -40,6 +41,7 @@ enum hmm_pfn_flags {
>>> HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
>>> HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
>>> HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
>>> + HMM_PFN_DEVICE_PRIVATE = 1UL << (BITS_PER_LONG - 7),
Doesn't this break HMM_PFN_ORDER_SHIFT? The assumption is that we have 5 bits
for
order
>>> /*
>>> * Sticky flags, carried from input to output,
>>> * don't forget to update HMM_PFN_INOUT_FLAGS
>>> diff --git a/mm/hmm.c b/mm/hmm.c
>>> index 87562914670a..1cff68ade1d4 100644
>>> --- a/mm/hmm.c
>>> +++ b/mm/hmm.c
>>> @@ -262,7 +262,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk,
>>> unsigned long addr,
>>> if (is_device_private_entry(entry) &&
>>> page_pgmap(pfn_swap_entry_to_page(entry))->owner ==
>>> range->dev_private_owner) {
>>> - cpu_flags = HMM_PFN_VALID;
>>> + cpu_flags = HMM_PFN_VALID | HMM_PFN_DEVICE_PRIVATE;
>>
>> I think you’ll need to set this flag in hmm_vma_handle_absent_pmd as
>> well. That function handles 2M device pages. Support for 2M device
>> pages, I believe, will be included in the 6.19 PR, but
>> hmm_vma_handle_absent_pmd is already upstream.
>
> Thanks Matt, I agree. There will be a few more updates to this
> series for 2MB device pages - I'll send the next revision on top of that
> support.
>
I think it makes sense to build on top of v6.19 with THP support
Balbir
