On 05.08.2025 11:52, Roger Pau Monne wrote:
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -275,7 +275,7 @@ static void __init assign_io_page(struct page_info *page)
>
> void __init arch_init_memory(void)
> {
> - unsigned long i, pfn, rstart_pfn, rend_pfn, iostart_pfn, ioend_pfn;
> + unsigned long i, pfn, rstart_pfn, rend_pfn, iostart_pfn, ioend_pfn, pdx;
>
> /*
> * Basic guest-accessible flags:
> @@ -328,9 +328,20 @@ void __init arch_init_memory(void)
> destroy_xen_mappings((unsigned long)mfn_to_virt(iostart_pfn),
> (unsigned long)mfn_to_virt(ioend_pfn));
>
> - /* Mark as I/O up to next RAM region. */
> - for ( ; pfn < rstart_pfn; pfn++ )
> + /*
> + * Mark as I/O up to next RAM region. Iterate over the PDX space to
> + * skip holes which would always fail the mfn_valid() check.
> + *
> + * pfn_to_pdx() requires a valid (iow: RAM) PFN to convert to PDX,
> + * hence provide pfn - 1, which is the tailing PFN from the last RAM
> + * range, or pdx 0 if the input pfn is 0.
> + */
> + for ( pdx = pfn ? pfn_to_pdx(pfn - 1) + 1 : 0;
> + pdx < pfn_to_pdx(rstart_pfn);
> + pdx++ )
> {
> + pfn = pdx_to_pfn(pdx);
> +
> if ( !mfn_valid(_mfn(pfn)) )
> continue;
>
As much as I would have liked to ack this, I fear there's another caveat here:
At the top of the loop we check not only for RAM, but also for UNUSABLE. The
latter, like RAM, shouldn't be marked I/O, but we also can't use PFN <-> PDX
transformations on any such page.
Jan
