[PATCH V5 1/3] riscv: mm: Prepare for reusing PTE RSW bit(9)

[Chunyan Zhang]

On Tue, 11 Feb 2025 at 12:01, Deepak Gupta <debug at rivosinc.com> wrote:
>
> On Tue, Feb 11, 2025 at 09:20:22AM +0800, Chunyan Zhang wrote:
> >On Thu, 30 Jan 2025 at 16:42, Björn Töpel <bjorn at kernel.org> wrote:
> >>
> >> Chunyan Zhang <zhangchunyan at iscas.ac.cn> writes:
> >>
> >> > The PTE bit(9) on RISC-V is reserved for software, it is used by devmap
> >> > now which has to be disabled if we want to use bit(9) for other features,
> >> > since there's no more free PTE bit on RISC-V now.
> >> >
> >> > So to make ARCH_HAS_PTE_DEVMAP selectable, this patch uses it as
> >> > the build condition of devmap definitions.
> >>
> >> Heads-up: It seems like Alistair's series [1] that removes the devmap
> >> PTE bit will most likely land in 6.15.
> >
> >Yes, I've been keeping an eye on Alistair's series, intended to update
> >this patchset after Alistair's patch that removes the devmap PTE bit
> >got merged.
>
> Please keep in mind that even after claiming back devmap PTE SW bit, a compile
> time decision to select between uffd-wp and soft-dirty is not desirable.

Yes, I agree. I've read your aother email. I also hope we can have
more RSW bits to use. So should we add uffd-wp and soft-dirty support
on RISC-V until we have two RSW bits for these two functions? Is an
undesirable solution better than no solution for now? I can optimize
the code when we have more free RSW bits, that's not hard.

Thanks,
Chunyan