Messages in this thread |  | | Date | Tue, 1 Nov 2016 09:46:41 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/cpuid: expose AVX512_4VNNIW and AVX512_4FMAPS features to kvm guest |
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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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