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),
/*
* 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.
Jordan.
Matt
if (is_writable_device_private_entry(entry))
cpu_flags |= HMM_PFN_WRITE;
new_pfn_flags = swp_offset_pfn(entry) | cpu_flags;
--
2.34.1
