Messages in this thread | | | Subject | Re: [patch 08/41] x86/fpu: Restrict fpstate sanitizing to legacy components | From | Andy Lutomirski <> | Date | Fri, 11 Jun 2021 12:03:37 -0700 |
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On 6/11/21 9:15 AM, Thomas Gleixner wrote: > xstateregs_get() does not longer use fpstate_sanitize_xstate() and the only
s/does not longer use/no longer uses/
\ > --- a/arch/x86/kernel/fpu/regset.c > +++ b/arch/x86/kernel/fpu/regset.c > @@ -11,6 +11,39 @@ > > #include <linux/sched/task_stack.h> > > +/* > + * When executing XSAVEOPT (or other optimized XSAVE instructions), if
The kernel doesn't use XSAVEOPT any more. How about:
When executing XSAVES (or other optimized XSAVE instructions)
> + * a processor implementation detects that an FPU state component is still > + * (or is again) in its initialized state, it may clear the corresponding > + * bit in the header.xfeatures field, and can skip the writeout of registers > + * to the corresponding memory layout.
Additionally, copy_xxx_to_xstate() may result in an xsave buffer with a bit clear in xfeatures but the corresponding state region not containing the state's init value.
> + * > + * This means that when the bit is zero, the state component might still > + * contain some previous - non-initialized register state.
Maybe say what the function does, e.g.:
This function fills in the init values for the X87 and SSE states if the corresponding xfeatures bits are clear.
> + * > + * This is required for the legacy regset functions. > + */ > +static void fpstate_sanitize_legacy(struct fpu *fpu) > +{ > + struct fxregs_state *fx = &fpu->state.fxsave; > + u64 xfeatures; > + > + if (!use_xsaveopt()) > + return;
This is confusing, since we never use xsaveopt. It's also wrong -- see above. How about just removing it?
> + > + xfeatures = fpu->state.xsave.header.xfeatures; > + > + /* If FP is in init state, reinitialize it */ > + if (!(xfeatures & XFEATURE_MASK_FP)) { > + memset(fx, 0, sizeof(*fx)); > + fx->cwd = 0x37f; > + } > + > + /* If SSE is in init state, clear the storage */ > + if (!(xfeatures & XFEATURE_MASK_SSE)) > + memset(fx->xmm_space, 0, sizeof(fx->xmm_space)); > +} > + >
Does this result in the mxcsr_mask and mxcsr fields being correct? There is a silly number of special cases there.
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