From: Paolo Bonzini <pbonzini@redhat.com>
To: Arthur Chunqi Li <yzt356@gmail.com>
Cc: kvm <kvm@vger.kernel.org>, Jan Kiszka <jan.kiszka@web.de>,
Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH 2/2] kvm-unit-tests: VMX: Test cases for nested EPT
Date: Mon, 09 Sep 2013 16:26:58 +0200 [thread overview]
Message-ID: <522DDAB2.9020900@redhat.com> (raw)
In-Reply-To: <CABpY8MJJg2hCqijPK0oL+z2g5_T2kewhtR7uk5tXB_tLj47WuQ@mail.gmail.com>
Il 09/09/2013 16:11, Arthur Chunqi Li ha scritto:
>>> >> +volatile u32 stage;
>>> >> +volatile bool init_fail;
>> >
>> > Why volatile?
> Because init_fail is only set but not used later in ept_init(), and if
> I don't add volatile, compiler may optimize the setting to init_fail.
>
> This occasion firstly occurred when I write set_stage/get_stage. If
> one variant is set in a function but not used later, the compiler
> usually optimizes this setting as redundant assignment and remove it.
No, the two are different. "stage" is written several times in the same
function, with no code in the middle:
stage++;
*p = 1;
stage++;
To the compiler, the first store is dead. The compiler doesn't know
that "*p = 1" traps to the hypervisor.
But this is not the case for "init_fail".
Paolo
next prev parent reply other threads:[~2013-09-09 14:26 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-09 4:57 [PATCH 0/2] kvm-unit-tests: VMX: Test nested EPT features Arthur Chunqi Li
2013-09-09 4:57 ` [PATCH 1/2] kvm-unit-tests: VMX: The framework of EPT for nested VMX testing Arthur Chunqi Li
2013-09-09 13:45 ` Paolo Bonzini
2013-09-09 4:57 ` [PATCH 2/2] kvm-unit-tests: VMX: Test cases for nested EPT Arthur Chunqi Li
2013-09-09 13:56 ` Paolo Bonzini
2013-09-09 14:11 ` Arthur Chunqi Li
2013-09-09 14:26 ` Paolo Bonzini [this message]
2013-09-09 15:29 ` Arthur Chunqi Li
2013-09-09 16:23 ` Paolo Bonzini
2013-09-09 7:17 ` [PATCH 0/2] kvm-unit-tests: VMX: Test nested EPT features Jan Kiszka
2013-09-09 7:44 ` Arthur Chunqi Li
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=522DDAB2.9020900@redhat.com \
--to=pbonzini@redhat.com \
--cc=gleb@redhat.com \
--cc=jan.kiszka@web.de \
--cc=kvm@vger.kernel.org \
--cc=yzt356@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox