Messages in this thread | | | Subject | Re: [PATCH] KVM: nVMX: expose INS/OUTS information support | From | Paolo Bonzini <> | Date | Mon, 5 Sep 2016 15:27:23 +0200 |
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On 05/09/2016 11:19, Yury Norov wrote: >> > >> > +static inline bool cpu_has_vmx_basic_inout(void) > inline is useless. See Documentation/CodingStyle, Chapter 15
No, it's not. See Documentation/CodingStyle, Chapter 15: "While the use of inlines can be appropriate (for example as a means of replacing macros, see Chapter 12), it very often is not".
>> > +{ >> > + return (((u64)vmcs_config.basic_cap << 32) & VMX_BASIC_INOUT); > You can shift VMX_BASIC_INOUT (at compile time) and avoid the shifting of > vmcs_config.basic_cap at runtime.
Not really since VMX_BASIC_INOUT comes from the processor manual.
It's ironic that your first remark places a lot of trust in the compiler, while the second places none. The compiler is happy to optimize away the left-shift/bitwise-AND pair to this:
movq %rdi, %rax shrq $22, %rax andl $1, %eax
where 22 is the order of VMX_BASIC_INOUT's only set bit, minus 32.
Paolo
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