On 27.03.2025 10:15, Jan Beulich wrote: > On 27.03.2025 09:21, Roger Pau Monné wrote: >> My main concern is whether the !mtrr path is still functional. Have >> you tried booting the resulting hypervisor with MTRR masked on CPUID? >> >> (or alternatively short-circuiting cpu_has_mtrr == 0?) > > I didn't think this would be a prereq here. If we boot in an environment truly > lacking MTRR, we'll crash on the first MTRR MSR access - none of those > accesses > use the safe accessors. Since you asked, I tried booting with "cpuid=no-mtrr". > As I'm doing this on a system with console, all I can say is that it takes > minutes to reach the point where we'd start setting up Dom0 (which itself then > takes so long that I timed out waiting for it to make progress), due to all > screen output becoming unbelievably slow after AP bringup. Surely something's > screwed somewhere, as VRAM accesses being slow (or fast) shouldn't depend on > AP > bringup having completed. I actually suspect it's not just VRAM accesses which > are slow, but that we're left running in uncachable mode altogether for > whatever > reason.
I think found a trivial way to avoid this, and the change there imo makes sense even if I can't explain this particular aspect of it. I'll submit that independently. Jan
