On Tue, Feb 02, 2021, Brijesh Singh wrote: > > On 2/2/21 10:02 AM, Kirill A. Shutemov wrote: > > On Mon, Feb 01, 2021 at 05:51:09PM -0800, David Rientjes wrote: > >> One possibility for minimal disruption to the boot entry code is to > >> require the guest BIOS to validate 4GB and below, and then leave 4GB and > >> above to be done lazily (the true amount of memory will actually be less > >> due to the MMIO hole). > > [ As I didn't looked into actual code, I may say total garbage below... ] > > > > Pre-validating 4GB would indeed be easiest way to go, but it's going to be > > too slow. > > > > The more realistic is for BIOS to pre-validate memory where kernel and > > initrd are placed, plus few dozen megs for runtime. It means decompression > > code would need to be aware about the validation. > > I was thinking that BIOS validating the lower 4GB will simplify the > changes to the kernel entry code path as well provide a clean approach > to support kexec. > > My initial thought is > > - BIOS or VMM validate lower 4GB memory. I think we need to treat this as a "plan for the worst, hope for the best" scenario. I agree that validating all of memory below 4gb would be simpler, but there's no guarantee that that approach will be fast enough. Even if it's sufficient for traditional VMs, inevitably someone will come up with a use case that wants/needs even shorter boot times.
