On Sun, May 16, 2021 at 12:09 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> That was the other problem fixed by this patch -- on big-endian 32-bit
> platforms with 64-bit dma_addr_t (mips, ppc), a DMA address with bit 32 set
> inadvertently sets the PageTail bit. So we need to store the low bits
> in the first word, even on big-endian platforms.
Ouch. And yes, that would have shot down the "dma page frame number" model too.
Oh how I wish PageTail was in "flags". Yes, our compound_head() thing
is "clever", but it's a pain,
That said, that union entry is "5 words", so the dma_addr_t thing
could easily just have had a dummy word at the beginning.
Linus
