On Wed, Sep 21, 2022, Gerd Hoffmann wrote: > On Fri, Sep 09, 2022 at 07:02:24AM +0200, Gerd Hoffmann wrote: > > On Thu, Sep 08, 2022 at 02:52:36PM +0000, Sean Christopherson wrote: > > > On Thu, Sep 08, 2022, Gerd Hoffmann wrote: > > > > -#define KVM_HINTS_REALTIME 0 > > > > +#define KVM_HINTS_REALTIME 0 > > > > +#define KVM_HINTS_PHYS_ADDRESS_SIZE_DATA_VALID 1 > > > > > > Why does KVM need to get involved? This is purely a userspace problem. > > > > It doesn't. I only need reserve a hints bit, and the canonical source > > for that happens to live in the kernel. That's why this patch doesn't > > touch any actual code ;) The issue is that this "hint" effectively breaks other VMMs that already provide an accurate guest.MAXPHYADDR. > > > E.g. why not use QEMU's fw_cfg to communicate this information to the > > > guest? > > > > That is indeed the other obvious way to implement this. Given this > > information will be needed in code paths which already do CPUID queries > > using CPUID to transport that information looked like the better option > > to me. > > I'd like to move forward with this. > > So, any comment further comments and opinions? > Is it ok to grab a hints bit given the explanation above? > Or should I go for the fw_cfg approach? My strong preference is the fw_cfg approach, or if the guest side really wants to use CPUID, have QEMU define it's own CPUID signature and provide QEMU-specific hints/quirks that way.
