Re: [PATCH 16/19] kvm: x86: Introduce KVM_{G|S}ET_XSAVE2 ioctl

Thomas Gleixner
2021-12-13T10:36:19Z

On Fri, Dec 10 2021 at 17:30, Paolo Bonzini wrote:
> On 12/8/21 01:03, Yang Zhong wrote:
>> +static int kvm_vcpu_ioctl_x86_set_xsave2(struct kvm_vcpu *vcpu, u8 *state)
>> +{
>> + if (fpstate_is_confidential(&vcpu->arch.guest_fpu))
>> + return 0;
>> +
>> + return fpu_copy_uabi_to_guest_fpstate(&vcpu->arch.guest_fpu, state,
>> + supported_xcr0, &vcpu->arch.pkru);
>> +}
>> +
>
> I think fpu_copy_uabi_to_guest_fpstate (and therefore
> copy_uabi_from_kernel_to_xstate) needs to check that the size is
> compatible with the components in the input.

fpu_copy_uabi_to_guest_fpstate() expects that the input buffer is
correctly sized. We surely can add a size check there.

> Also, IIUC the size of the AMX state will vary in different processors.
> Is this correct? If so, this should be handled already by
> KVM_GET/SET_XSAVE2 and therefore should be part of the
> arch/x86/kernel/fpu APIs. In the future we want to support migrating a
> "small AMX" host to a "large AMX" host; and also migrating from a "large
> AMX" host to a "small AMX" host if the guest CPUID is compatible with
> the destination of the migration.

How is that supposed to work? If the AMX state size differs then the
hosts are not compatible.

Thanks,

tglx