linux-kernel - Re: [PATCH v2 3/3] KVM: remove dummy pages

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Message-Id: <20120726185214.d8235761.yoshikawa.takuya@oss.ntt.co.jp>
Date:	Thu, 26 Jul 2012 18:52:14 +0900
From:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] KVM: remove dummy pages

On Thu, 26 Jul 2012 17:35:13 +0800
Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:

> > Is this patch really safe for all architectures?
> > 
> > IS_ERR_VALUE() casts -MAX_ERRNO to unsigned long and then does comparison.
> > Isn't it possible to conflict with valid pfns?
> > 
> 
> See IS_ERR_VALUE():
> 
> #define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
> 
> The minimal value of the error code is:
> 0xffff f001 on 32-bit and 0x ffff ffff ffff f001 on 64-bit,
> it is fair larger that a valid pfn (for the pfn, the most top of 12 bits
> are always 0).
> 
> Note, PAE is a special case, but only 64G physical memory is valid,
> 0xffff f001 is also suitable for that.

Ah, I see.  I misread the type pfn_t and was confused.
Thank you!

	Takuya
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