Re: [MINI-OS PATCH v2 1/2] mm: provide a way to do very early page table allocations

[Jürgen Groß <jgross@xxxxxxxx>]

On 29.07.25 10:52, Jan Beulich wrote:
> On 29.07.2025 10:38, Juergen Gross wrote:
> > --- a/arch/x86/mm.c
> > +++ b/arch/x86/mm.c
> > @@ -640,13 +640,20 @@ void change_readonly(bool readonly)
> >   /*
> >    * return a valid PTE for a given virtual address. If PTE does not exist,
> >    * allocate page-table pages.
> > + * Provide a small pool for allocating some page tables very early. Those are
> > + * needed currently for mapping the shared info page, so 2 pages ought to be
> > + * enough. Add one spare page anyway.
> >    */
> Hmm, 2 pages plus one spare doesn't yield ...
>
> > +static char early_pt[4][PAGE_SIZE] __attribute__((aligned(PAGE_SIZE)));
> ... 4. Was 2 a typo, and 3 was meant? (Which, just to mention it, then isn't
> correct for 32-bit aiui.) Whatever adjustment wants making - happy to do so
> while committing. Just need to know which way. Then
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Thanks. Should have been 3, of course. And even on 32-bit 3 are enough. :-)


Juergen

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