On 2/16/22 08:48, Leonardo Bras Soares Passos wrote:
On Mon, Feb 14, 2022 at 6:56 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
On top of this patch, we can even replace vcpu->arch.guest_supported_xcr0
with vcpu->arch.guest_fpu.fpstate->user_xfeatures. Probably with local
variables or wrapper functions though, so as to keep the code readable.
You mean another patch (#2) removing guest_supported_xcr0 field from
kvm_vcpu_arch ?
(and introducing something like kvm_guest_supported_xcr() ?)
Yes, introducing both kvm_guest_supported_xcr0() that just reads
user_xfeatures, and kvm_guest_supported_xfd() as below.
For example:
static inline u64 kvm_guest_supported_xfd()
{
u64 guest_supported_xcr0 = vcpu->arch.guest_fpu.fpstate->user_xfeatures;
return guest_supported_xcr0 & XFEATURE_MASK_USER_DYNAMIC;
}
Not sure If I get the above.
Are you suggesting also removing fpstate->xfd and use a wrapper instead?
Or is the above just an example?
(s/xfd/xcr0/ & s/XFEATURE_MASK_USER_DYNAMIC/XFEATURE_MASK_USER_SUPPORTED/ )
The above is an example of how even "indirect" uses as
guest_supported_xcr0 can be changed to a function.
Also, already in this patch fpstate_realloc should do
newfps->user_xfeatures = curfps->user_xfeatures | xfeatures;
only if !guest_fpu. In other words, the user_xfeatures of the guest FPU
should be controlled exclusively by KVM_SET_CPUID2.
Just to check, you suggest adding this on patch #2 ?
(I am failing to see how would that impact on #1)
In patch 1. Since KVM_SET_CPUID2 now changes newfps->user_xfeatures, it
should be the only place where it's changed, and arch_prctl() should not
change it anymore.
Paolo
