Re: [PATCH] x86/hvm: don't treat MMIO pages as special ones regarding cache attributes

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.09.2020 13:05, Roger Pau Monné wrote:
> It's still not clear to me what option would be better: modify
> share_xen_page_with_guest to not mark pages as Xen heap, or implement
> something different to assign MMIO pages to dom_io without setting
> the Xen heap flag.

static void __init share_io_page(struct page_info *page)
{
    set_gpfn_from_mfn(mfn_x(page_to_mfn(page)), INVALID_M2P_ENTRY);

    /* The incremented type count pins as writable. */
    page->u.inuse.type_info = PGT_writable_page | PGT_validated | 1;

    page_set_owner(page, dom_io);

    page->count_info |= PGC_allocated | 1;
}

is of course much shorter than share_xen_page_with_guest(), but
I'm nevertheless uncertain whether simply making conditional
the setting of PGC_xen_heap there isn't the easier route. Of
course, not pointlessly acquiring and releasing a lock has its
own appeal.

Jan