From: Paul Durrant <Paul.Durrant@citrix.com>
To: 'Jan Beulich' <JBeulich@suse.com>
Cc: Juergen Gross <jgross@suse.com>,
Andrew Cooper <Andrew.Cooper3@citrix.com>,
"Julien Grall (julien.grall@arm.com)" <julien.grall@arm.com>,
'BorisOstrovsky' <boris.ostrovsky@oracle.com>,
"xen-devel(xen-devel@lists.xenproject.org)"
<xen-devel@lists.xenproject.org>
Subject: Re: debian stretch dom0 + xen 4.9 fails to boot
Date: Thu, 8 Jun 2017 13:24:38 +0000 [thread overview]
Message-ID: <ccbaede636924bbab1a26a2b53c626e2@AMSPEX02CL03.citrite.net> (raw)
In-Reply-To: <59396AE10200007800160D0E@prv-mh.provo.novell.com>
> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: 08 June 2017 14:19
> To: Paul Durrant <Paul.Durrant@citrix.com>
> Cc: Julien Grall (julien.grall@arm.com) <julien.grall@arm.com>; Andrew
> Cooper <Andrew.Cooper3@citrix.com>; xen-devel(xen-
> devel@lists.xenproject.org) <xen-devel@lists.xenproject.org>;
> 'BorisOstrovsky' <boris.ostrovsky@oracle.com>; Juergen Gross
> <jgross@suse.com>
> Subject: RE: [Xen-devel] debian stretch dom0 + xen 4.9 fails to boot
>
> >>> On 08.06.17 at 14:42, <Paul.Durrant@citrix.com> wrote:
> > For those following this...
> >
> > By poking characters at the screen and bisecting where they stopped, I
> have
> > narrowed the problem to the code in edd.S. I can successfully boot by
> setting
> > opt_edd=off on the Xen cmd line and I can also boot with the following
> patch
> > applied:
> >
> > diff --git a/xen/arch/x86/boot/edd.S b/xen/arch/x86/boot/edd.S
> > index 73371f98b5..5409f1d9a1 100644
> > --- a/xen/arch/x86/boot/edd.S
> > +++ b/xen/arch/x86/boot/edd.S
> > @@ -148,5 +148,6 @@ GLOBAL(boot_mbr_signature_nr)
> > .byte 0
> > GLOBAL(boot_mbr_signature)
> > .fill EDD_MBR_SIG_MAX*8,1,0
> > + .align 4096
> > GLOBAL(boot_edd_info)
> > - .fill 512,1,0 # big enough for a disc
> > sector
> > + .fill 4096,1,0 # big enough for a disc
> > sector
> >
> > (based on a hunch that the BIOS defaults to a 4K sector for my NVMe drive)
> >
> > I need to investigate some more but I do wonder whether the EDD info
> should
> > be read first to determine the appropriate size of memory buffer to use
> when
> > issuing the read of the MBR. Hardcoding a 4k reservation seems like the
> wrong
> > thing to do, even if it is sufficient for this BIOS.
>
> boot_edd_info is being used for two things - reading the MBR of
> each disk and storing data retrieved from INT 13 Fn 41 and 48.
> The latter occupies 492 bytes (6 times 8+74). Which would make
> me guess the system has a 4k disk, and the BIOS doesn't abstract
> away this characteristic when handling INT 13 Fn 02 (which is
> supposed to only act in multiples of 512-byte sectors, as opposed
> to Fn 42).
>
> The alternative of Fn 48 overflowing its buffer would seem less
> likely, especially with the buffer holding a size on input.
Yes, I tested with edd=skipmbr on the command line (and no patch applied) and the system booted, so it's definitely the MBR read that is at fault.
>
> Do you, btw, really need both the size and alignment increases?
>
At first I tried just increasing the .fill to 4096 but that did not seem to work. I have not found anything that says int13 0x2 buffers need to be aligned... but the BIOS being buggy in this respect I guess it could easily require that.
I'm just testing some more code to try to see exactly how much memory the MBR read scribbles on.
Paul
> Jan
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next prev parent reply other threads:[~2017-06-08 13:24 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-06 14:32 debian stretch dom0 + xen 4.9 fails to boot Paul Durrant
2017-06-06 15:11 ` Jan Beulich
2017-06-06 15:51 ` Paul Durrant
2017-06-06 16:28 ` Paul Durrant
2017-06-06 17:00 ` Boris Ostrovsky
2017-06-07 8:07 ` Jan Beulich
2017-06-07 8:09 ` Paul Durrant
2017-06-07 8:19 ` Paul Durrant
2017-06-07 14:05 ` Boris Ostrovsky
2017-06-07 8:07 ` Paul Durrant
2017-06-07 8:27 ` Jan Beulich
[not found] ` <5937D4FF02000078001602F6@suse.com>
2017-06-07 9:03 ` Juergen Gross
2017-06-07 9:05 ` Paul Durrant
2017-06-07 9:09 ` Andrew Cooper
2017-06-07 10:36 ` Paul Durrant
2017-06-07 11:06 ` Paul Durrant
2017-06-07 11:57 ` Juergen Gross
2017-06-07 12:02 ` Paul Durrant
2017-06-07 12:13 ` Juergen Gross
2017-06-07 12:19 ` Jan Beulich
2017-06-07 12:26 ` Paul Durrant
2017-06-07 12:34 ` Jan Beulich
2017-06-07 11:50 ` Jan Beulich
2017-06-07 11:55 ` Paul Durrant
2017-06-07 12:00 ` Jan Beulich
2017-06-07 12:46 ` Paul Durrant
2017-06-07 12:55 ` Jan Beulich
2017-06-07 15:06 ` Paul Durrant
2017-06-07 15:33 ` Jan Beulich
2017-06-07 15:40 ` Paul Durrant
2017-06-07 15:52 ` Jan Beulich
2017-06-08 12:42 ` Paul Durrant
2017-06-08 12:46 ` Juergen Gross
2017-06-08 13:18 ` Jan Beulich
2017-06-08 13:24 ` Paul Durrant [this message]
2017-06-09 12:19 ` Paul Durrant
2017-06-09 13:05 ` Jan Beulich
2017-06-09 13:52 ` Boris Ostrovsky
2017-06-09 15:14 ` Paul Durrant
2017-06-09 15:41 ` Jan Beulich
2017-06-09 15:47 ` Paul Durrant
2017-06-09 15:58 ` Jan Beulich
2017-06-12 8:14 ` Paul Durrant
2017-06-12 10:40 ` Jan Beulich
2017-06-12 10:44 ` Paul Durrant
2017-06-12 10:53 ` Paul Durrant
2017-06-12 11:12 ` Jan Beulich
2017-06-12 12:05 ` Paul Durrant
2017-06-12 12:25 ` Paul Durrant
2017-06-12 13:54 ` Jan Beulich
2017-06-12 14:28 ` Paul Durrant
2017-06-12 14:43 ` Paul Durrant
2017-06-12 15:03 ` Paul Durrant
2017-06-12 15:07 ` Jan Beulich
2017-06-12 15:21 ` Paul Durrant
2017-06-06 17:40 ` Julien Grall
2017-06-07 8:05 ` Paul Durrant
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