2016-11-25 16:11+0100, David Hildenbrand: > Am 25.11.2016 um 15:51 schrieb Radim Krčmář: >> The guest could have configured a maximal physical address that exceeds >> the host. Prevent that situation as it could easily lead to a bug. >> >> Signed-off-by: Radim Krčmář <[email protected]> >> --- >> arch/x86/kvm/cpuid.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c >> index 25f0f15fab1a..aed910e9fbed 100644 >> --- a/arch/x86/kvm/cpuid.c >> +++ b/arch/x86/kvm/cpuid.c >> @@ -136,7 +136,13 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu) >> ((best->eax & 0xff00) >> 8) != 0) >> return -EINVAL; >> >> - /* Update physical-address width */ >> + >> + /* >> + * Update physical-address width. >> + * Make sure that it does not exceed hardware capabilities. >> + */ >> + if (cpuid_query_maxphyaddr(vcpu) > boot_cpu_data.x86_phys_bits) > > The name maxphyaddr is really misleading. But that is a different story.
Yes, I'll rename it, thanks. > This check is correct. > > However, I wonder if there is any way for user space to query this property? Do you mean boot_cpu_data.x86_phys_bits? Userspace can execute CPUID instruction and read the value; QEMU does. > On s390x, there is a kvm capability to export this information to user > space. So QEMU can fail (e.g. migration) with a nice error message about > missing hardware support. > > (most probably we still want to block this case, as migration will seem to > work but than simply fail due to missing hardware support I guess). Maybe > there is also already a nice check in QEMU that I am not yet aware of :) This patch is bad. It would break QEMU on all old machines, because QEMU sets 40 by default. Heh, QEMU doesn't check at all -- it even allows migration with "host-phys-bits" feature and will happily change phys-bits when migrating to another machine.
