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Bae" , Zide Chen , Xudong Hao , Peter Fang , Zhao Liu Subject: Re: [PATCH 4/5] i386/cpu: Support APX CPUIDs Message-ID: References: <20251118065817.835017-1-zhao1.liu@intel.com> <20251118065817.835017-5-zhao1.liu@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=gb2312 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: > Please just make the new leaf have constant values based on just > APX_F. We'll add the optional NCI/NDD/NF support if needed, i.e. > never. :) Maybe not never? > > Note, APX_NCI_NDD_NF is documented as always enabled for Intel > > processors since APX spec (revision v7.0). Now any Intel processor > > that enumerates support for APX_F (CPUID.(EAX=0x7, ECX=1).EDX[21]) > > will also enumerate support for APX_NCI_NDD_NF. This sentence (from APX spec rev.7) emphasizes the ¡°Intel¡± vendor, and its primary goal was to address and explain compatibility concern for pre-enabling work based on APX spec v6. Prior to v7, APX included NCI_NDD_NF by default, but this feature has now been separated from basic APX and requires explicit checking CPUID bit. x86 ecosystem advisory group has aligned on APX so it may be possible for other x86 vendors to implement APX without NCI_NDD_NF and this still match with the APX spec. If we default to setting this NCI_NDD_NF bit for APX, then in the future when we run into other vendors that don't support this feature, we'll not only have to make it optional again, but we'll also need to do fixes similar to the ARCH_CAPABILITIES situation - checking vendors, fixing compatibility issues, and all that stuff. Therefore, compared to default setting to constant, I think the optional NCI_NDD_NF now not only aligns with arch spec but also prevents future compatibility issues. :) Thanks, Zhao