On 29.04.2025 12:48, Alejandro Vallejo wrote: > On Tue Apr 29, 2025 at 9:28 AM BST, Jan Beulich wrote: >> On 28.04.2025 21:57, Ariadne Conill wrote: >>> Previously Xen placed the hypercall page at the highest possible MFN, >>> but this caused problems on systems where there is more than 36 bits >>> of physical address space. >> >> Hmm, I should have asked already on the earlier version: What kinds of >> problems are these, beyond ... >> >>> In general, it also seems unreliable to assume that the highest possible >>> MFN is not already reserved for some other purpose. >> >> ... this particular aspect? I find it puzzling that such problems would >> depend on the number of physical address bits. > > Pagefault on access (due to reserved bits being set) on access to the > hypercall page. The available guest-physical address space doesn't seem > to be as wide as advertised, though I didn't carry enough tests to > single this as the only explanation. Seeing how we don't really know > what's already on the last mfn this seems like a strict improvement > irrespective of the actual cause of the fault.
No question there, yet the first paragraph is a little too vague for my taste. It'll also not help people later finding this commit and wondering what the issue was. Jan
