From: Paul Mackerras <paulus@ozlabs.org>
To: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Balbir Singh <bsingharora@gmail.com>, linuxppc-dev@lists.ozlabs.org
Subject: Re: Fix BUG_ON() reporting in real mode on powerpc
Date: Wed, 17 Feb 2016 19:23:47 +1100 [thread overview]
Message-ID: <20160217082347.GA19495@fergus.ozlabs.ibm.com> (raw)
In-Reply-To: <56C42954.3000801@linux.vnet.ibm.com>
On Wed, Feb 17, 2016 at 01:33:32PM +0530, Anshuman Khandual wrote:
> On 02/17/2016 12:46 PM, Balbir Singh wrote:
> >> > It might be a little better to do this:
> >> >
> >> > bugaddr = regs->nip;
> >> > if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR))
> >> > bugaddr += PAGE_OFFSET;
> >> >
> >> > It is possible to execute from addresses with the 0xc000... on top in
> >> > real mode, because the CPU ignores the top 4 address bits in real
> >> > mode.
> > Good catch! Thank you
> >
> > Changelog:
> > Don't add PAGE_OFFSET blindly, check if REGION_ID is 0
>
> Cant we use USER_REGION_ID directly ?
If we use USER_REGION_ID then the reader needs to know that the user
region is region 0 to understand the code. Thus I think it is clearer
to use REGION_ID(bugaddr) == 0. Whether or not the address is a user
region address is not really relevant to the question of whether it's
a physical address being accessed directly in real mode vs. a kernel
virtual address, which is what we're trying to determine.
Paul.
next prev parent reply other threads:[~2016-02-17 8:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-17 4:43 Fix BUG_ON() reporting in real mode on powerpc Balbir Singh
2016-02-17 4:56 ` Paul Mackerras
2016-02-17 7:16 ` Balbir Singh
2016-02-17 8:03 ` Anshuman Khandual
2016-02-17 8:23 ` Paul Mackerras [this message]
2016-02-17 15:16 ` Aneesh Kumar K.V
2016-02-18 0:25 ` Balbir Singh
2016-02-18 2:41 ` Aneesh Kumar K.V
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