From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: Is it safe to assume that v == current in
	hvm_do_resume()?
Date: Wed, 22 Oct 2014 10:04:59 +0100
Message-ID: <5447733B.6010300@citrix.com>
References: <544766BD.4020009@bitdefender.com>
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To: Razvan Cojocaru <rcojocaru@bitdefender.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
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On 22/10/14 09:11, Razvan Cojocaru wrote:
> Hello,
>
> As far as I've understood the code, and based on several tests, it would
> appear that in xen/arch/x86/hvm/hvm.c, the struct vcpu *v parameter to
> hvm_do_resume() is always equal to current.
>
> Is that a reasonable assumption to make? I could have missed some use
> cases for the function.

The calls look like this:

{vmx,svm}_do_resume is the schedule_tail function pointer, which is a
no-return function and called on the way out of a context switch.

They call hvm_do_resume() followed by a reset_stack_and_jump() to
{vmx,svm}_asm_do_vmentry.

So yes - you can be guaranteed that the v in hvm_do_resume() is current.

If you do come to explicitly rely on this behaviour, and it is in any
way unclear, it might be worth introducing an ASSERT(v == current) near
to the expectation.

~Andrew