On Thu Apr 24, 2025 at 1:45 PM BST, Alejandro Vallejo wrote:
> Xen nowadays crashes under some Hyper-V configurations when
> paddr_bits>36. At the 44bit boundary we reach an edge case in which the
> end of the guest physical address space is not representable using 32bit
> MFNs. Furthermore, it's an act of faith that the tail of the physical
> address space has no reserved regions already.
>
> This commit uses the first unused MFN rather than the last, thus
> ensuring the hypercall page placement is more resilient against such
> corner cases.
>
> While at this, add an extra BUG_ON() to explicitly test for the
> hypercall page being correctly set, and mark hcall_page_ready as
> __ro_after_init.
>
> Fixes: 620fc734f854("x86/hyperv: setup hypercall page")
> Signed-off-by: Alejandro Vallejo <agarc...@amd.com>After a side discussion, this seems on the unsafe side of things due to potential collision with MMIO. I'll resend (though not today) with the page overlapping a RAM page instead. Possibly the last page of actual RAM. Cheers, Alejandro
