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Darwish" Cc: Dave Hansen , Ingo Molnar , Thomas Gleixner , Andrew Cooper , "H. Peter Anvin" , Christian Ludloff , Maciej Wieczor-Retman , Sohil Mehta , John Ogness , x86@kernel.org, x86-cpuid@lists.linux.dev, LKML Subject: Re: [PATCH v7 013/120] x86/cpu: Use parsed CPUID(0x80000000) Message-ID: <20260602012321.GFah4wid2xSkjbicDJ@fat_crate.local> References: <20260528153923.403473-1-darwi@linutronix.de> <20260528153923.403473-14-darwi@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260528153923.403473-14-darwi@linutronix.de> On Thu, May 28, 2026 at 05:37:35PM +0200, Ahmed S. Darwish wrote: > At early boot code, use parsed CPUID(0x80000000) instead of invoking a > direct CPUID query. > > The original code has the check: > > extended_cpuid_level = ((eax & 0xffff0000) == 0x80000000) ? eax : 0; > > to protect against Intel 32-bit machines without an extended range, where a > CPUID(0x80000000) query will repeat the output of the max-valid standard > CPUID leaf output. > > A similar check is already done at the CPUID parser's own CPUID(0x80000000) > read function: > > if (CPUID_RANGE(el0->max_ext_leaf) != CPUID_EXT_START) { > // Handle error > } > > Thus, for the call-site, the parsed CPUID NULL check below: > > el0 = cpuid_leaf(c, 0x80000000); > extended_cpuid_level = el0 ? el0->max_ext_leaf : 0; > > is sufficient. I don't think this needs the code examples - just explain that the check is done by the parser now. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette