* Eduardo Habkost (ehabk...@redhat.com) wrote:
> On Tue, Jul 05, 2016 at 08:03:18PM +0100, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> >
> > A special case based on the previous phys-bits property; if it's
> > the magic value 0 then use the hosts capabilities.
> >
> > We can also use the value we read from the host to check the users
> > explicitly set value and warn them if it doesn't match.
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> > ---
> > target-i386/cpu.c | 53
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 53 insertions(+)
> >
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index f33cf58..6ebd26b 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -2952,7 +2952,60 @@ static void x86_cpu_realizefn(DeviceState *dev,
> > Error **errp)
> > & CPUID_EXT2_AMD_ALIASES);
> > }
> >
> > + /* For 64bit systems think about the number of physical bits to
> > present.
> > + * ideally this should be the same as the host; anything other than
> > matching
> > + * the host can cause incorrect guest behaviour.
> > + * QEMU used to pick the magic value of 40 bits that corresponds to
> > + * consumer AMD devices but nothing esle.
> > + */
> > if (env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
> > + if (kvm_enabled()) {
> > + /* Read the hosts physical address size, and compare it to
> > what we
> > + * were asked for; note old machine types default to 40 bits
> > + */
>
> Isn't the "old machine types default to 40 bits" part obsolete,
> now that you use 9999 to indicate it was not set explicitly?
Yes it is; gone.
> Also, the observation makes me confused: I know the old machine
> types default to 40 bits, but I don't know why I need to know
> that to understand the host_cpuid() logic below.
Yes that comment also made more sense the way it used to be arranged.
>
> > + uint32_t eax;
> > + uint32_t host_phys_bits = 0;
> > + static bool warned;
> > +
> > + host_cpuid(0x80000000, 0, &eax, NULL, NULL, NULL);
> > + if (eax >= 0x80000008) {
> > + host_cpuid(0x80000008, 0, &eax, NULL, NULL, NULL);
> > + /* Note: According to AMD doc 25481 rev 2.34 they have a
> > field
> > + * at 23:16 that can specify a maximum physical address
> > bits for
> > + * the guest that can override this value; but I've not
> > seen
> > + * anything with that set.
> > + */
> > + host_phys_bits = eax & 0xff;
> > + } else {
> > + /* It's an odd 64 bit machine that doesn't have the leaf
> > for
> > + * physical address bits; fall back to 36 that's most older
> > + * Intel.
> > + */
> > + host_phys_bits = 36;
> > + }
>
> I would love to see this logic moved inside a
> x86_host_phys_bits() function.
Done.
> > +
> > + if (cpu->phys_bits == 0) {
> > + /* The user asked for us to use the host physical bits */
> > + cpu->phys_bits = host_phys_bits;
> > + }
> > +
> > + /* Print a warning if the user set it to a value that's not the
> > + * host value.
> > + */
> > + if (cpu->phys_bits != host_phys_bits && cpu->phys_bits != 9999
> > &&
> > + !warned) {
> > + error_report("Warning: Host physical bits (%u)"
> > + " does not match phys_bits (%u)",
> > + host_phys_bits, cpu->phys_bits);
> > + warned = true;
>
> The name of the user-visible property is "phys-bits", not
> phys_bits. Maybe we could say "does not match phys-bits
> property".
Done.
Dave
>
> > + }
> > + } else {
> > + if (cpu->phys_bits == 0) {
> > + error_setg(errp, "phys_bits can not be read from the host
> > in"
> > + " TCG mode");
> > + return;
> > + }
> > + }
> > /* 9999 is a special meaning 'use the old default',
> > */
> > if (cpu->phys_bits == 9999) {
> > --
> > 2.7.4
> >
>
> --
> Eduardo
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
