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Thu, 13 Nov 2025 23:23:39 +0000 Message-ID: Date: Thu, 13 Nov 2025 15:23:37 -0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v1 10/20] KVM: x86: Refactor REX prefix handling in instruction emulation To: Paolo Bonzini , , CC: , , References: <20251110180131.28264-1-chang.seok.bae@intel.com> <20251110180131.28264-11-chang.seok.bae@intel.com> Content-Language: en-US From: "Chang S. 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Bae > Date:   Mon Nov 10 18:01:21 2025 +0000 > >     KVM: x86: Refactor REX prefix handling in instruction emulation >     Restructure how to represent and interpret REX fields, preparing >     for handling of VEX and REX2. >     REX uses the upper four bits of a single byte as a fixed identifier, >     and the lower four bits containing the data. VEX and REX2 extend > this so >     that the first byte identifies the prefix and the rest encode > additional >     bits; and while VEX only has the same four data bits as REX, eight > zero >     bits are a valid value for the data bits of REX2.  So, stop storing > the >     REX byte as-is.  Instead, store only the low bits of the REX prefix > and >     track separately whether a REX-like prefix wasused. >     No functional changes intended. >     Signed-off-by: Chang S. Bae >     Message-ID: <20251110180131.28264-11-chang.seok.bae@intel.com> >     [Extracted from APX series; removed bitfields and REX2-specific >      definitions. - Paolo] >     Signed-off-by: Paolo Bonzini Sure, I think it's good to have consistent handling like this for these extended prefixes across the board. Thanks!