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Date: Tue, 1 Nov 2016 09:46:41 +0100 From: Borislav Petkov <bp@...en8.de> To: He Chen <he.chen@...ux.intel.com> Cc: Paolo Bonzini <pbonzini@...hat.com>, "Luc, Piotr" <Piotr.Luc@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>, "mingo@...hat.com" <mingo@...hat.com>, "Kang, Luwei" <luwei.kang@...el.com>, "rkrcmar@...hat.com" <rkrcmar@...hat.com> Subject: Re: [PATCH] x86/cpuid: expose AVX512_4VNNIW and AVX512_4FMAPS features to kvm guest On Tue, Nov 01, 2016 at 03:48:50PM +0800, He Chen wrote: > Before sending a patch, let me check if my understanding is right... > I will add a helper in scattered.c like: > > unsigned int get_scattered_cpuid_features(unsigned int level, > unsigned int sub_leaf, enum cpuid_regs reg) > { > u32 val = 0; > const struct cpuid_bit *cb; > > for (cb = cpuid_bits; cb->feature; cb++) { Right, we can improve that by keeping cpuid_bit.level sorted so that you can break out early if the level is exceeded. For that please sort it and add a comment stating that the leaf should be kept sorted ontop of it. And then you do something like this: u32 get_scattered_cpuid_leaf(unsigned int level, unsigned int sub_leaf, enum cpuid_regs reg) { u32 cpuid_val = 0; for (cb = cpuid_bits; cb->feature; cb++) { if (level < cb->level) continue; if (level > cb->level) break; if (cb->reg == reg && sub_leaf == cb->sub_leaf) { if (cpu_has(cb->feature)) cpuid_val |= BIT(cb->bit); } } return cpuid_val; } Completely untested, of course. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply.
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