Re: [PATCH v3 1/2] x86/mm: add API for marking only part of a MMIO page read only

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, May 22, 2024 at 03:29:51PM +0200, Jan Beulich wrote:
> On 22.05.2024 15:22, Marek Marczykowski-Górecki wrote:
> > On Wed, May 22, 2024 at 09:52:44AM +0200, Jan Beulich wrote:
> >> On 21.05.2024 04:54, Marek Marczykowski-Górecki wrote:
> >>> +static void subpage_mmio_write_emulate(
> >>> +    mfn_t mfn,
> >>> +    unsigned int offset,
> >>> +    const void *data,
> >>> +    unsigned int len)
> >>> +{
> >>> +    struct subpage_ro_range *entry;
> >>> +    void __iomem *addr;
> >>
> >> Wouldn't this better be pointer-to-volatile, with ...
> > 
> > Shouldn't then most other uses of __iomem in the code base be this way
> > too? I see volatile only in few places...
> 
> Quite likely, yet being consistent at least in new code is going to be
> at least desirable.

I tried. Build fails because iounmap() doesn't declare its argument as
volatile, so it triggers -Werror=discarded-qualifiers...

I'll change it just in subpage_mmio_write_emulate(), but leave
subpage_mmio_map_page() (was _get_page) without volatile.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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