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From: Steven Price <steven.price@arm.com>
To: Mark Rutland <mark.rutland@arm.com>, Christoph Hellwig <hch@lst.de>
Cc: linux-kernel@vger.kernel.org, Mike Rapoport <rppt@linux.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Will Deacon <will.deacon@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>
Subject: Re: Bad virt_to_phys since commit 54c7a8916a887f35
Date: Thu, 16 May 2019 15:05:31 +0100	[thread overview]
Message-ID: <e70ead93-2fe9-faf9-9e77-9df15809bad6@arm.com> (raw)
In-Reply-To: <20190516134105.GB43059@lakrids.cambridge.arm.com>

On 16/05/2019 14:41, Mark Rutland wrote:
> On Thu, May 16, 2019 at 02:38:20PM +0100, Mark Rutland wrote:
>> Hi,
>>
>> Since commit:
>>
>>   54c7a8916a887f35 ("initramfs: free initrd memory if opening /initrd.image fails")
> 
> Ugh, I dropped a paragarph here.
> 
> Since that commit, I'm seeing a boot-time splat on arm64 when using
> CONFIG_DEBUG_VIRTUAL. I'm running an arm64 syzkaller instance, and this
> kills the VM, preventing further testing, which is unfortunate.
> 
> Mark.
> 
>> IIUC prior to that commit, we'd only attempt to free an intird if we had
>> one, whereas now we do so unconditionally. AFAICT, in this case
>> initrd_start has not been initialized (I'm not using an initrd or
>> initramfs on my system), so we end up trying virt_to_phys() on a bogus
>> VA in free_initrd_mem().
>>
>> Any ideas on the right way to fix this?

Your analysis looks right to me. In my review I'd managed to spot the
change in behaviour when CONFIG_INITRAMFS_FORCE is set (the initrd is
freed), but I'd overlooked what happens if initrd_start == 0 (the
non-existent initrd is attempted to be freed).

I suspect the following is sufficient to fix the problem:

----8<-----
diff --git a/init/initramfs.c b/init/initramfs.c
index 435a428c2af1..178130fd61c2 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -669,7 +669,7 @@ static int __init populate_rootfs(void)
 	 * If the initrd region is overlapped with crashkernel reserved region,
 	 * free only memory that is not part of crashkernel region.
 	 */
-	if (!do_retain_initrd && !kexec_free_initrd())
+	if (!do_retain_initrd && initrd_start && !kexec_free_initrd())
 		free_initrd_mem(initrd_start, initrd_end);
 	initrd_start = 0;
 	initrd_end = 0;

  reply	other threads:[~2019-05-16 14:05 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16 13:38 Mark Rutland
2019-05-16 13:41 ` Mark Rutland
2019-05-16 14:05   ` Steven Price [this message]
2019-05-16 14:16     ` Mark Rutland
2019-05-16 14:20       ` Steven Price
2019-05-16 14:27         ` Mark Rutland
2019-05-23  9:31         ` Will Deacon
2019-05-23  9:54           ` Mike Rapoport
2019-05-23  9:58             ` Steven Price
2019-05-23 10:01               ` Will Deacon
2019-05-16 14:13   ` Mike Rapoport
2019-05-16 14:21     ` Mark Rutland
2019-05-16 14:23       ` Christoph Hellwig

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