[PATCH 1/2] md: Add PCI_P2PDMA support for MD RAID volumes

[Keith Busch]

On Tue, Mar 24, 2026 at 09:13:55PM +0000, Kiran Modukuri wrote:
> Hi Christoph,
> 
> We tested with RAID0 , RAID1 and RAID10 only. You're right that parity RAID personalities
> need CPU access to data pages for XOR/parity computation, which won't
> work with P2P mappings.
> 
> 
> We'll send a v2 that moves BLK_FEAT_PCI_P2PDMA out of
> md_init_stacking_limits() and instead has raid0, raid1 and raid10
> opt in individually during their queue limits setup. raid4/5/6 will
> not set the flag.

I think the parity could work with P2P memory if the calculation is
offloaded to a dma_aysnc_tx. It doesn't look like we necessarily know if
any particular xor is going to get offloaded, though.