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Thu, 15 Jan 2026 23:43:08 +0000 Message-ID: Date: Thu, 15 Jan 2026 15:43:06 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] x86/fpu: Clear XSTATE_BV[i] in save state whenever XFD[i]=1 To: Dave Hansen , Paolo Bonzini , , CC: , , Thomas Gleixner , Borislav Petkov References: <20260101090516.316883-1-pbonzini@redhat.com> <20260101090516.316883-2-pbonzini@redhat.com> <8ee84cb9-ef6d-43ac-b9d0-9c22e7d1ecd8@redhat.com> Content-Language: en-US From: "Chang S. 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Kinda like the language that's already in > "XRSTOR and the Init and Modified Optimizations", but specific to XFD: > > If XFD[i] = 1 and XINUSE[i] = 1, state component i may be > tracked as init; XINUSE[i] may be set to 0. > > That would make it consistent with the KVM behavior. It might also give > the CPU folks some additional wiggle room for new behavior. Yeah, I saw that you quoted this sentence in the XFD section in your other response: If XSAVE, XSAVEC, XSAVEOPT, or XSAVES is saving the state component i, the instruction does not generate #NM when XCR0[i] = IA32_XFD[i] = 1; instead, it operates as if XINUSE[i] = 0 (and the state component was in its initial state) Indeed, I do applaud the idea to clarify this behavior more explicitly right there. Thanks, Chang