On Mon, Jul 04, 2016 at 08:16:05PM +0100, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>
> The CPU GPs if we try and set a bit in a variable MTRR mask above
> the limit of physical address bits on the host. We hit this
> when loading a migration from a host with a larger physical
> address limit than our destination (e.g. a Xeon->i7 of same
> generation) but previously used to get away with it
> until 48e1a45 started checking that msr writes actually worked.
>
> It seems in our case the GP probably comes from KVM emulating
> that GP.
>
> Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> target-i386/kvm.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index f3698f1..6429205 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -1677,6 +1677,8 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
> }
> }
> if (has_msr_mtrr) {
> + uint64_t phys_mask = MAKE_64BIT_MASK(0, cpu->phys_bits);
> +
> kvm_msr_entry_add(cpu, MSR_MTRRdefType, env->mtrr_deftype);
> kvm_msr_entry_add(cpu, MSR_MTRRfix64K_00000, env->mtrr_fixed[0]);
> kvm_msr_entry_add(cpu, MSR_MTRRfix16K_80000, env->mtrr_fixed[1]);
> @@ -1690,10 +1692,15 @@ static int kvm_put_msrs(X86CPU *cpu, int level)
> kvm_msr_entry_add(cpu, MSR_MTRRfix4K_F0000, env->mtrr_fixed[9]);
> kvm_msr_entry_add(cpu, MSR_MTRRfix4K_F8000, env->mtrr_fixed[10]);
> for (i = 0; i < MSR_MTRRcap_VCNT; i++) {
> + /* The CPU GPs if we write to a bit above the physical limit
> of
> + * the host CPU (and KVM emulates that)
> + */
> + uint64_t mask = env->mtrr_var[i].mask;
> + mask &= phys_mask;
> +
I was arguing that we should print warnings when we really had to
change the MTRR values on migration.
But if we are already inside kvm_put_msrs() with a different
phys_bits value, the best we can do is to trim the bits so they
still make sense. If we want to print a warning, this can be done
somewhere else.
Reviewed-by: Eduardo Habkost <ehabk...@redhat.com>
> kvm_msr_entry_add(cpu, MSR_MTRRphysBase(i),
> env->mtrr_var[i].base);
> - kvm_msr_entry_add(cpu, MSR_MTRRphysMask(i),
> - env->mtrr_var[i].mask);
> + kvm_msr_entry_add(cpu, MSR_MTRRphysMask(i), mask);
> }
> }
>
> --
> 2.7.4
>
--
Eduardo
