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Date: Thu, 20 Oct 2022 09:57:28 -0700 From: Dave Hansen <dave.hansen@...el.com> To: "Chang S. Bae" <chang.seok.bae@...el.com>, linux-kernel@...r.kernel.org Cc: x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, yuan.yao@...el.com Subject: Re: [PATCH 1/1] x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly On 10/18/22 15:13, Chang S. Bae wrote: > @@ -1141,10 +1141,14 @@ void __copy_xstate_to_uabi_buf(struct membuf to, struct fpstate *fpstate, > */ > pkru.pkru = pkru_val; > membuf_write(&to, &pkru, sizeof(pkru)); > + } else if (!(header.xfeatures & BIT_ULL(i))) { > + /* > + * Every extended state component has an all zeros > + * init state. > + */ > + membuf_zero(&to, xstate_sizes[i]); > } else { > - copy_feature(header.xfeatures & BIT_ULL(i), &to, > - __raw_xsave_addr(xsave, i), > - __raw_xsave_addr(xinit, i), > + membuf_write(&to, __raw_xsave_addr(xsave, i), > xstate_sizes[i]); > } Just to add a bit more context, this is inside this loop: mask = fpstate->user_xfeatures; for_each_extended_xfeature(i, mask) { if (zerofrom < xstate_offsets[i]) membuf_zero(&to, xstate_offsets[i] - zerofrom); ... } if (to.left) membuf_zero(&to, to.left); In other words, the loop and the surrounding code already know how to membuf_zero() any gaps in the middle or the end of the user buffer. Would it be simpler to just adjust the 'mask' over which the loop iterates? I think that would end up being something like: mask = fpstate->user_xfeatures & (xsave->xfeatures | xinit->xfeatures); Logically, that makes sense too. We're copying out of either 'xsave' or 'xinit'. If a feature isn't in either one of those we can't do the copy_feature() on it.
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