From: Paolo Bonzini <pbonzini@redhat.com>
To: Yury Norov <ynorov@caviumnetworks.com>,
Jan Dakinevich <jan.dakinevich@gmail.com>
Cc: kvm@vger.kernel.org, rkrcmar@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] KVM: nVMX: expose INS/OUTS information support
Date: Mon, 5 Sep 2016 15:27:23 +0200 [thread overview]
Message-ID: <f027aa22-b7ee-88a4-4b1d-6bef77bd5a16@redhat.com> (raw)
In-Reply-To: <20160905091913.GA22817@yury-N73SV>
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
next prev parent reply other threads:[~2016-09-05 13:36 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-04 18:23 Jan Dakinevich
2016-09-05 9:19 ` Yury Norov
2016-09-05 13:27 ` Paolo Bonzini [this message]
2016-09-05 13:27 ` Paolo Bonzini
2016-09-05 14:47 ` [PATCH v2] " Jan Dakinevich
2016-09-05 14:50 ` Paolo Bonzini
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