Re: [PATCH 05/19] x86/fpu: Move xfd initialization out of __fpstate_reset() to the callers

Thomas Gleixner
2021-12-10T22:33:21Z

Yang, Jing,

On Tue, Dec 07 2021 at 19:03, Yang Zhong wrote:
> diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
> index fe592799508c..fae44fa27cdb 100644
> --- a/arch/x86/kernel/fpu/core.c
> +++ b/arch/x86/kernel/fpu/core.c
> @@ -231,6 +231,7 @@ bool fpu_alloc_guest_fpstate(struct fpu_guest *gfpu)
> if (!fpstate)
> return false;
>
> + /* Leave xfd to 0 (the reset value defined by spec) */
> __fpstate_reset(fpstate);

That change makes me a bit wary simply because the comment here is above
__fpstate_reset() which makes no sense. It does make sense to you at the
time, but does it make sense to you when you look at it 6 month down the
road?

So I'd rather make this very obvious what's going. See below.

Thanks,

tglx
---

--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -199,7 +199,7 @@ void fpu_reset_from_exception_fixup(void
}

#if IS_ENABLED(CONFIG_KVM)
-static void __fpstate_reset(struct fpstate *fpstate);
+static void __fpstate_reset(struct fpstate *fpstate, u64 xfd);

static void fpu_init_guest_permissions(struct fpu_guest *gfpu)
{
@@ -231,7 +231,8 @@ bool fpu_alloc_guest_fpstate(struct fpu_
if (!fpstate)
return false;

- __fpstate_reset(fpstate);
+ /* Leave xfd to 0 (the reset value defined by spec) */
+ __fpstate_reset(fpstate, 0);
fpstate_init_user(fpstate);
fpstate->is_valloc = true;
fpstate->is_guest = true;
@@ -454,21 +455,21 @@ void fpstate_init_user(struct fpstate *f
fpstate_init_fstate(fpstate);
}

-static void __fpstate_reset(struct fpstate *fpstate)
+static void __fpstate_reset(struct fpstate *fpstate, u64 xfd)
{
/* Initialize sizes and feature masks */
fpstate->size = fpu_kernel_cfg.default_size;
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 = init_fpstate.xfd;
+ fpstate->xfd = xfd;
}

void fpstate_reset(struct fpu *fpu)
{
/* Set the fpstate pointer to the default fpstate */
fpu->fpstate = &fpu->__fpstate;
- __fpstate_reset(fpu->fpstate);
+ __fpstate_reset(fpu->fpstate, init_fpstate.xfd);

/* Initialize the permission related info in fpu */
fpu->perm.__state_perm = fpu_kernel_cfg.default_features;