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Peter Anvin" , Eric Biggers , Kees Cook Content-Type: text/plain; charset="us-ascii" On Mon, May 12, 2025, Chao Gao wrote: > @@ -535,10 +538,20 @@ void fpstate_init_user(struct fpstate *fpstate) > > static void __fpstate_reset(struct fpstate *fpstate, u64 xfd) > { > - /* Initialize sizes and feature masks */ > - fpstate->size = fpu_kernel_cfg.default_size; > + /* > + * Initialize sizes and feature masks. Supervisor features and > + * sizes may diverge between guest FPUs and host FPUs, whereas > + * user features and sizes are always identical the same. Pick of of "identical" or "the same" :-) And maybe explain why supervisor features can diverge, while the kernel ensures user features are identical? Ditto for the XFD divergence. E.g. I think this would be accurate (though I may be reading too much into user features): /* * Supervisor features (and thus sizes) may diverge between guest FPUs * and host FPUs, as some supervisor features are supported for guests * despite not being utilized by the host. User features and sizes are * always identical, which allows for common guest and userspace ABI. * * For the host, set XFD to the kernel's desired initialization value. * For guests, set XFD to its architectural RESET value. */ > + */ > + if (fpstate->is_guest) { > + fpstate->size = guest_default_cfg.size; > + fpstate->xfeatures = guest_default_cfg.features; > + } else { > + fpstate->size = fpu_kernel_cfg.default_size; > + fpstate->xfeatures = fpu_kernel_cfg.default_features; > + } > + > fpstate->user_size = fpu_user_cfg.default_size; > - fpstate->xfeatures = fpu_kernel_cfg.default_features; > fpstate->user_xfeatures = fpu_user_cfg.default_features; > fpstate->xfd = xfd; > } > -- > 2.47.1 >