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?
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.
> + 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.
> +
> + 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".
> + }
> + } 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
