On Fri, 07 Jan 2022 18:48:16 +0000, Peter Maydell <peter.maydell@xxxxxxxxxx> wrote: > > On Fri, 7 Jan 2022 at 18:18, Marc Zyngier <maz@xxxxxxxxxx> wrote: > > This is a chicken and egg problem: you need the IPA size to compute > > the memory map, and you need the memory map to compute the IPA > > size. Fun, isn't it? > > > > At the moment, virt_set_memmap() doesn't know about the IPA space, > > generates a highest_gpa that may not work, and we end-up failing > > because the resulting VM type is out of bound. > > > > My solution to that is to feed the *maximum* IPA size to > > virt_set_memmap(), compute the memory map there, and then use > > highest_gpa to compute the actual IPA size that is used to create the > > VM. By knowing the IPA limit in virt_set_memmap(), I'm able to keep it > > in check and avoid generating an unusable memory map. > > Is there any reason not to just always create the VM with the > maximum supported IPA size, rather than trying to create it > with the smallest IPA size that will work? (ie skip the last > step of computing the IPA size to create the VM with) That gives KVM the opportunity to reduce the depth of the S2 page tables. On HW that supports a large PA space, there is a real advantage in keeping these shallow if at all possible. Thanks, M. -- Without deviation from the norm, progress is not possible.
