On 12/8/21 01:03, Yang Zhong wrote:
+ u64 xcr0 = vcpu->arch.xcr0 & XFEATURE_MASK_USER_DYNAMIC;
+
+ /* For any state which is enabled dynamically */
+ if ((xfd & xcr0) != xcr0) {
+ u64 request = (xcr0 ^ xfd) & xcr0;
+ struct fpu_guest *guest_fpu = &vcpu->arch.guest_fpu;
+
+ /*
+ * If requested features haven't been enabled, update
+ * the request bitmap and tell the caller to request
+ * dynamic buffer reallocation.
+ */
+ if ((guest_fpu->user_xfeatures & request) != request) {
+ vcpu->arch.guest_fpu.realloc_request = request;
This should be "|=". If you have
wrmsr(XFD, dynamic-feature-1);
...
wrmsr(XFD, dynamic-feature-2);
then the space for both features has to be allocated.
+ return true;
+ }
+ }
+
This is just:
struct fpu_guest *guest_fpu = &vcpu->arch.guest_fpu;
u64 xcr0 = vcpu->arch.xcr0 & XFEATURE_MASK_USER_DYNAMIC;
u64 dynamic_enabled = xcr0 & ~xfd;
if (!(dynamic_enabled & ~guest_fpu->user_xfeatures))
return false;
/*
* This should actually not be in guest_fpu, see review of
* patch 2. Also see above regarding "=" vs "|=".
*/
vcpu->arch.guest_fpu.realloc_request |= dynamic_enabled;
return true;
But without documentation I'm not sure why this exit-to-userspace step
is needed:
- if (dynamic_enabled & ~guest_fpu->user_perm) != 0, then this is a
userspace error and you can #GP the guest without any issue. Userspace
is buggy
- if (dynamic_enabled & ~guest_fpu->user_xfeatures) != 0, but the
feature *is* permitted, then it is okay to just go on and reallocate the
guest FPU.
Paolo
