* Re: Loading a 32 bit kernel from 64 bit grub-xen
2014-07-01 18:27 ` Phillip Susi
@ 2014-07-01 18:33 ` Vladimir 'phcoder' Serbinenko
2014-07-01 18:33 ` Vladimir 'phcoder' Serbinenko
` (4 subsequent siblings)
5 siblings, 0 replies; 18+ messages in thread
From: Vladimir 'phcoder' Serbinenko @ 2014-07-01 18:33 UTC (permalink / raw)
To: The development of GRUB 2; +Cc: Andrey Borzenkov, xen-devel
[-- Attachment #1.1: Type: text/plain, Size: 2420 bytes --]
On 1 Jul 2014 20:28, "Phillip Susi" <psusi@ubuntu.com> wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> > В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> > пишет:
> >
> >> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >
> >> I have been trying to fix grub to load a 32 bit kernel from the
> >> 64 bit xen build. After fixing up one or two minor issues with
> >> the elf loader, I believe I now have it to the point where it
> >> jumps correctly to the 32 bit kernel and it crashes there, since
> >> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >> question is how to return the cpu to 32 bit mode *under xen*?
> >
> >
> > IIRC it was already discussed not long ago and it seems to be Xen
> > limitation. You probably need to ask on xen-devel to be sure.
> >
> > Is it not more simple to use 32 bit grub with 32 bit kernel to
> > start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. That makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary.
Binaries don't have to use e.g. paging table or hypercall mechanism. You
need to either make xen switch all those structures or port kernels to
fake-32-xen mode. When either is done GRUB part will be trivial but either
of those tasks is outside of grub scope.
> I suppose I'll
> Cc xen-devel.
>
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> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
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_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: Loading a 32 bit kernel from 64 bit grub-xen
2014-07-01 18:27 ` Phillip Susi
2014-07-01 18:33 ` Vladimir 'phcoder' Serbinenko
@ 2014-07-01 18:33 ` Vladimir 'phcoder' Serbinenko
2014-07-02 8:35 ` Jan Beulich
` (3 subsequent siblings)
5 siblings, 0 replies; 18+ messages in thread
From: Vladimir 'phcoder' Serbinenko @ 2014-07-01 18:33 UTC (permalink / raw)
To: The development of GRUB 2; +Cc: Andrey Borzenkov, xen-devel
[-- Attachment #1: Type: text/plain, Size: 2420 bytes --]
On 1 Jul 2014 20:28, "Phillip Susi" <psusi@ubuntu.com> wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> > В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> > пишет:
> >
> >> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >
> >> I have been trying to fix grub to load a 32 bit kernel from the
> >> 64 bit xen build. After fixing up one or two minor issues with
> >> the elf loader, I believe I now have it to the point where it
> >> jumps correctly to the 32 bit kernel and it crashes there, since
> >> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >> question is how to return the cpu to 32 bit mode *under xen*?
> >
> >
> > IIRC it was already discussed not long ago and it seems to be Xen
> > limitation. You probably need to ask on xen-devel to be sure.
> >
> > Is it not more simple to use 32 bit grub with 32 bit kernel to
> > start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. That makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary.
Binaries don't have to use e.g. paging table or hypercall mechanism. You
need to either make xen switch all those structures or port kernels to
fake-32-xen mode. When either is done GRUB part will be trivial but either
of those tasks is outside of grub scope.
> I suppose I'll
> Cc xen-devel.
>
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> Version: GnuPG v2.0.17 (MingW32)
> Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
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> -----END PGP SIGNATURE-----
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
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^ permalink raw reply [flat|nested] 18+ messages in thread* Re: Loading a 32 bit kernel from 64 bit grub-xen
2014-07-01 18:27 ` Phillip Susi
2014-07-01 18:33 ` Vladimir 'phcoder' Serbinenko
2014-07-01 18:33 ` Vladimir 'phcoder' Serbinenko
@ 2014-07-02 8:35 ` Jan Beulich
2014-07-02 8:35 ` [Xen-devel] " Jan Beulich
` (2 subsequent siblings)
5 siblings, 0 replies; 18+ messages in thread
From: Jan Beulich @ 2014-07-02 8:35 UTC (permalink / raw)
To: Phillip Susi
Cc: Andrey Borzenkov, The development of GNU GRUB, Daniel Kiper,
xen-devel
>>> On 01.07.14 at 20:27, <psusi@ubuntu.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
>> В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
>> пишет:
>>
>>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
>>
>>> I have been trying to fix grub to load a 32 bit kernel from the
>>> 64 bit xen build. After fixing up one or two minor issues with
>>> the elf loader, I believe I now have it to the point where it
>>> jumps correctly to the 32 bit kernel and it crashes there, since
>>> it is 32 bit code still executing on a cpu in 64 bit mode. The
>>> question is how to return the cpu to 32 bit mode *under xen*?
>>
>>
>> IIRC it was already discussed not long ago and it seems to be Xen
>> limitation. You probably need to ask on xen-devel to be sure.
>>
>> Is it not more simple to use 32 bit grub with 32 bit kernel to
>> start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. That makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> Cc xen-devel.
Perhaps there's some confusion about what "kernel" here means:
The thing that's the kernel from GrUB's perspective is the hypervisor,
i.e. xen.gz or xen.efi. While the former expects to be entered in 32-bit
mode, on the Xen side we all agree that this isn't the way things
should work under UEFI; Daniel already proposed how to handle this
case (Xen should be entered in 64-bit mode, with ExitBootServices()
not having got called yet).
The thing that you'd traditionally call kernel (e.g. Linux) can be 32-
or 64-bit irrespective of GrUB's bitness: Xen knows how to load either
(both for Dom0 and, likely irrelevant here, DomU).
Jan
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
2014-07-01 18:27 ` Phillip Susi
` (2 preceding siblings ...)
2014-07-02 8:35 ` Jan Beulich
@ 2014-07-02 8:35 ` Jan Beulich
2014-07-02 8:38 ` Vladimir 'phcoder' Serbinenko
` (2 more replies)
2014-07-02 9:26 ` [Xen-devel] " Ian Campbell
2014-07-02 9:26 ` Ian Campbell
5 siblings, 3 replies; 18+ messages in thread
From: Jan Beulich @ 2014-07-02 8:35 UTC (permalink / raw)
To: Phillip Susi
Cc: Andrey Borzenkov, The development of GNU GRUB, Daniel Kiper,
xen-devel
>>> On 01.07.14 at 20:27, <psusi@ubuntu.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
>> В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
>> пишет:
>>
>>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
>>
>>> I have been trying to fix grub to load a 32 bit kernel from the
>>> 64 bit xen build. After fixing up one or two minor issues with
>>> the elf loader, I believe I now have it to the point where it
>>> jumps correctly to the 32 bit kernel and it crashes there, since
>>> it is 32 bit code still executing on a cpu in 64 bit mode. The
>>> question is how to return the cpu to 32 bit mode *under xen*?
>>
>>
>> IIRC it was already discussed not long ago and it seems to be Xen
>> limitation. You probably need to ask on xen-devel to be sure.
>>
>> Is it not more simple to use 32 bit grub with 32 bit kernel to
>> start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. That makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> Cc xen-devel.
Perhaps there's some confusion about what "kernel" here means:
The thing that's the kernel from GrUB's perspective is the hypervisor,
i.e. xen.gz or xen.efi. While the former expects to be entered in 32-bit
mode, on the Xen side we all agree that this isn't the way things
should work under UEFI; Daniel already proposed how to handle this
case (Xen should be entered in 64-bit mode, with ExitBootServices()
not having got called yet).
The thing that you'd traditionally call kernel (e.g. Linux) can be 32-
or 64-bit irrespective of GrUB's bitness: Xen knows how to load either
(both for Dom0 and, likely irrelevant here, DomU).
Jan
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
2014-07-02 8:35 ` [Xen-devel] " Jan Beulich
@ 2014-07-02 8:38 ` Vladimir 'phcoder' Serbinenko
2014-07-02 9:27 ` Ian Campbell
2014-07-02 9:27 ` Ian Campbell
2 siblings, 0 replies; 18+ messages in thread
From: Vladimir 'phcoder' Serbinenko @ 2014-07-02 8:38 UTC (permalink / raw)
To: The development of GRUB 2
[-- Attachment #1: Type: text/plain, Size: 2428 bytes --]
On 2 Jul 2014 10:36, "Jan Beulich" <JBeulich@suse.com> wrote:
>
> >>> On 01.07.14 at 20:27, <psusi@ubuntu.com> wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> >> В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> >> пишет:
> >>
> >>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >>
> >>> I have been trying to fix grub to load a 32 bit kernel from the
> >>> 64 bit xen build. After fixing up one or two minor issues with
> >>> the elf loader, I believe I now have it to the point where it
> >>> jumps correctly to the 32 bit kernel and it crashes there, since
> >>> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >>> question is how to return the cpu to 32 bit mode *under xen*?
> >>
> >>
> >> IIRC it was already discussed not long ago and it seems to be Xen
> >> limitation. You probably need to ask on xen-devel to be sure.
> >>
> >> Is it not more simple to use 32 bit grub with 32 bit kernel to
> >> start with?
> >
> > The problem with that is that you have to know in advance which kernel
> > you are going to boot. That makes configuring virtual hosts harder;
> > they just want one grub image they can use to chainload whatever the
> > guest wants to install in their domain.
> >
> > Also there must be a way to do this otherwise a 64 bit kernel running
> > under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> > Cc xen-devel.
>
> Perhaps there's some confusion about what "kernel" here means:
> The thing that's the kernel from GrUB's perspective is the hypervisor,
> i.e. xen.gz or xen.efi. While the former expects to be entered in 32-bit
> mode, on the Xen side we all agree that this isn't the way things
> should work under UEFI; Daniel already proposed how to handle this
> case (Xen should be entered in 64-bit mode, with ExitBootServices()
> not having got called yet).
>
> The thing that you'd traditionally call kernel (e.g. Linux) can be 32-
> or 64-bit irrespective of GrUB's bitness: Xen knows how to load either
> (both for Dom0 and, likely irrelevant here, DomU).
>
Actually you're the first one to speak about dom0 here. Whole discussion
was about domU.
> Jan
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
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^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
2014-07-02 8:35 ` [Xen-devel] " Jan Beulich
2014-07-02 8:38 ` Vladimir 'phcoder' Serbinenko
@ 2014-07-02 9:27 ` Ian Campbell
2014-07-02 9:27 ` Ian Campbell
2 siblings, 0 replies; 18+ messages in thread
From: Ian Campbell @ 2014-07-02 9:27 UTC (permalink / raw)
To: Jan Beulich
Cc: Phillip Susi, Andrey Borzenkov, Daniel Kiper, xen-devel,
The development of GNU GRUB
On Wed, 2014-07-02 at 09:35 +0100, Jan Beulich wrote:
> >>> On 01.07.14 at 20:27, <psusi@ubuntu.com> wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> >> В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> >> пишет:
> >>
> >>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >>
> >>> I have been trying to fix grub to load a 32 bit kernel from the
> >>> 64 bit xen build. After fixing up one or two minor issues with
> >>> the elf loader, I believe I now have it to the point where it
> >>> jumps correctly to the 32 bit kernel and it crashes there, since
> >>> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >>> question is how to return the cpu to 32 bit mode *under xen*?
> >>
> >>
> >> IIRC it was already discussed not long ago and it seems to be Xen
> >> limitation. You probably need to ask on xen-devel to be sure.
> >>
> >> Is it not more simple to use 32 bit grub with 32 bit kernel to
> >> start with?
> >
> > The problem with that is that you have to know in advance which kernel
> > you are going to boot. That makes configuring virtual hosts harder;
> > they just want one grub image they can use to chainload whatever the
> > guest wants to install in their domain.
> >
> > Also there must be a way to do this otherwise a 64 bit kernel running
> > under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> > Cc xen-devel.
>
> Perhaps there's some confusion about what "kernel" here means:
> The thing that's the kernel from GrUB's perspective is the hypervisor,
> i.e. xen.gz or xen.efi. While the former expects to be entered in 32-bit
> mode, on the Xen side we all agree that this isn't the way things
> should work under UEFI; Daniel already proposed how to handle this
> case (Xen should be entered in 64-bit mode, with ExitBootServices()
> not having got called yet).
>
> The thing that you'd traditionally call kernel (e.g. Linux) can be 32-
> or 64-bit irrespective of GrUB's bitness: Xen knows how to load either
> (both for Dom0 and, likely irrelevant here, DomU).
Actually, I read Philips message as refering to launching a domU kernel
from a PV grub-xen, not a dom0 thing.
Ian
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: Loading a 32 bit kernel from 64 bit grub-xen
2014-07-02 8:35 ` [Xen-devel] " Jan Beulich
2014-07-02 8:38 ` Vladimir 'phcoder' Serbinenko
2014-07-02 9:27 ` Ian Campbell
@ 2014-07-02 9:27 ` Ian Campbell
2 siblings, 0 replies; 18+ messages in thread
From: Ian Campbell @ 2014-07-02 9:27 UTC (permalink / raw)
To: Jan Beulich
Cc: Phillip Susi, Andrey Borzenkov, Daniel Kiper, xen-devel,
The development of GNU GRUB
On Wed, 2014-07-02 at 09:35 +0100, Jan Beulich wrote:
> >>> On 01.07.14 at 20:27, <psusi@ubuntu.com> wrote:
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> >> В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> >> пишет:
> >>
> >>> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >>
> >>> I have been trying to fix grub to load a 32 bit kernel from the
> >>> 64 bit xen build. After fixing up one or two minor issues with
> >>> the elf loader, I believe I now have it to the point where it
> >>> jumps correctly to the 32 bit kernel and it crashes there, since
> >>> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >>> question is how to return the cpu to 32 bit mode *under xen*?
> >>
> >>
> >> IIRC it was already discussed not long ago and it seems to be Xen
> >> limitation. You probably need to ask on xen-devel to be sure.
> >>
> >> Is it not more simple to use 32 bit grub with 32 bit kernel to
> >> start with?
> >
> > The problem with that is that you have to know in advance which kernel
> > you are going to boot. That makes configuring virtual hosts harder;
> > they just want one grub image they can use to chainload whatever the
> > guest wants to install in their domain.
> >
> > Also there must be a way to do this otherwise a 64 bit kernel running
> > under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> > Cc xen-devel.
>
> Perhaps there's some confusion about what "kernel" here means:
> The thing that's the kernel from GrUB's perspective is the hypervisor,
> i.e. xen.gz or xen.efi. While the former expects to be entered in 32-bit
> mode, on the Xen side we all agree that this isn't the way things
> should work under UEFI; Daniel already proposed how to handle this
> case (Xen should be entered in 64-bit mode, with ExitBootServices()
> not having got called yet).
>
> The thing that you'd traditionally call kernel (e.g. Linux) can be 32-
> or 64-bit irrespective of GrUB's bitness: Xen knows how to load either
> (both for Dom0 and, likely irrelevant here, DomU).
Actually, I read Philips message as refering to launching a domU kernel
from a PV grub-xen, not a dom0 thing.
Ian
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
2014-07-01 18:27 ` Phillip Susi
` (3 preceding siblings ...)
2014-07-02 8:35 ` [Xen-devel] " Jan Beulich
@ 2014-07-02 9:26 ` Ian Campbell
2014-07-08 15:37 ` Phillip Susi
2014-07-02 9:26 ` Ian Campbell
5 siblings, 1 reply; 18+ messages in thread
From: Ian Campbell @ 2014-07-02 9:26 UTC (permalink / raw)
To: Phillip Susi; +Cc: Andrey Borzenkov, The development of GNU GRUB, xen-devel
On Tue, 2014-07-01 at 14:27 -0400, Phillip Susi wrote:
> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> > В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> > пишет:
> >
> >> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >
> >> I have been trying to fix grub to load a 32 bit kernel from the
> >> 64 bit xen build. After fixing up one or two minor issues with
> >> the elf loader, I believe I now have it to the point where it
> >> jumps correctly to the 32 bit kernel and it crashes there, since
> >> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >> question is how to return the cpu to 32 bit mode *under xen*?
> >
> >
> > IIRC it was already discussed not long ago and it seems to be Xen
> > limitation. You probably need to ask on xen-devel to be sure.
> >
> > Is it not more simple to use 32 bit grub with 32 bit kernel to
> > start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. That makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> Cc xen-devel.
Running a 32-bit userspace under a 64-bit kernel is a very different
thing to switching a kernel from 64-bit down to 32-bit (or vice versa).
While the former is of course supported just fine the latter is not and
IIRC doing so would be very difficult for a PV kernel due to the way the
interfaces are constructed (e.g. to p2m entries change size, the maximum
addressable machine address changes).
Yes, this is a massive Pain In The A**.
Ian.
^ permalink raw reply [flat|nested] 18+ messages in thread* Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
2014-07-02 9:26 ` [Xen-devel] " Ian Campbell
@ 2014-07-08 15:37 ` Phillip Susi
0 siblings, 0 replies; 18+ messages in thread
From: Phillip Susi @ 2014-07-08 15:37 UTC (permalink / raw)
To: Ian Campbell; +Cc: Andrey Borzenkov, The development of GNU GRUB, xen-devel
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On 7/2/2014 5:26 AM, Ian Campbell wrote:
So you are saying that you could put the cpu into 32 bit mode, but xen
would still believe that the domU is 64 bit, and thus, expect the
hypercalls to be 64 bit?
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^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: Loading a 32 bit kernel from 64 bit grub-xen
@ 2014-07-08 15:37 ` Phillip Susi
0 siblings, 0 replies; 18+ messages in thread
From: Phillip Susi @ 2014-07-08 15:37 UTC (permalink / raw)
To: Ian Campbell; +Cc: Andrey Borzenkov, The development of GNU GRUB, xen-devel
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Hash: SHA1
On 7/2/2014 5:26 AM, Ian Campbell wrote:
So you are saying that you could put the cpu into 32 bit mode, but xen
would still believe that the domU is 64 bit, and thus, expect the
hypercalls to be 64 bit?
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^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: [Xen-devel] Loading a 32 bit kernel from 64 bit grub-xen
2014-07-08 15:37 ` Phillip Susi
(?)
@ 2014-07-08 15:47 ` Ian Campbell
-1 siblings, 0 replies; 18+ messages in thread
From: Ian Campbell @ 2014-07-08 15:47 UTC (permalink / raw)
To: Phillip Susi; +Cc: Andrey Borzenkov, The development of GNU GRUB, xen-devel
On Tue, 2014-07-08 at 11:37 -0400, Phillip Susi wrote:
> On 7/2/2014 5:26 AM, Ian Campbell wrote:
>
> So you are saying
I don't know, because you've helpfully trimmed all of the context of
something I said a week ago.
/me consults list archive, I think you are responding to:
> > Running a 32-bit userspace under a 64-bit kernel is a very different
> > thing to switching a kernel from 64-bit down to 32-bit (or vice versa).
> >
> > While the former is of course supported just fine the latter is not and
> > IIRC doing so would be very difficult for a PV kernel due to the way the
> > interfaces are constructed (e.g. to p2m entries change size, the maximum
> > addressable machine address changes).
----
> that you could put the cpu into 32 bit mode, but xen
> would still believe that the domU is 64 bit, and thus, expect the
> hypercalls to be 64 bit?
Assuming you are asking about 32-bit kernel mode then a Xen PV 64-bit
guest cannot be transitioned to run in kernel mode in anything other
than 64-bit mode. There is simply no way to put the cpu into 32 bit mode
while remaining in kernel mode.
If you meant in userspace then all userspace hypercalls are made via a
kernel driver and thus appear to come from the 64-bit kernel and Xen
sees them as such.
Ian.
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: Loading a 32 bit kernel from 64 bit grub-xen
2014-07-08 15:37 ` Phillip Susi
(?)
(?)
@ 2014-07-08 15:47 ` Ian Campbell
-1 siblings, 0 replies; 18+ messages in thread
From: Ian Campbell @ 2014-07-08 15:47 UTC (permalink / raw)
To: Phillip Susi; +Cc: Andrey Borzenkov, The development of GNU GRUB, xen-devel
On Tue, 2014-07-08 at 11:37 -0400, Phillip Susi wrote:
> On 7/2/2014 5:26 AM, Ian Campbell wrote:
>
> So you are saying
I don't know, because you've helpfully trimmed all of the context of
something I said a week ago.
/me consults list archive, I think you are responding to:
> > Running a 32-bit userspace under a 64-bit kernel is a very different
> > thing to switching a kernel from 64-bit down to 32-bit (or vice versa).
> >
> > While the former is of course supported just fine the latter is not and
> > IIRC doing so would be very difficult for a PV kernel due to the way the
> > interfaces are constructed (e.g. to p2m entries change size, the maximum
> > addressable machine address changes).
----
> that you could put the cpu into 32 bit mode, but xen
> would still believe that the domU is 64 bit, and thus, expect the
> hypercalls to be 64 bit?
Assuming you are asking about 32-bit kernel mode then a Xen PV 64-bit
guest cannot be transitioned to run in kernel mode in anything other
than 64-bit mode. There is simply no way to put the cpu into 32 bit mode
while remaining in kernel mode.
If you meant in userspace then all userspace hypercalls are made via a
kernel driver and thus appear to come from the 64-bit kernel and Xen
sees them as such.
Ian.
^ permalink raw reply [flat|nested] 18+ messages in thread
* Re: Loading a 32 bit kernel from 64 bit grub-xen
2014-07-01 18:27 ` Phillip Susi
` (4 preceding siblings ...)
2014-07-02 9:26 ` [Xen-devel] " Ian Campbell
@ 2014-07-02 9:26 ` Ian Campbell
5 siblings, 0 replies; 18+ messages in thread
From: Ian Campbell @ 2014-07-02 9:26 UTC (permalink / raw)
To: Phillip Susi; +Cc: Andrey Borzenkov, The development of GNU GRUB, xen-devel
On Tue, 2014-07-01 at 14:27 -0400, Phillip Susi wrote:
> On 7/1/2014 12:18 PM, Andrey Borzenkov wrote:
> > В Tue, 01 Jul 2014 12:06:08 -0400 Phillip Susi <psusi@ubuntu.com>
> > пишет:
> >
> >> -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
> >
> >> I have been trying to fix grub to load a 32 bit kernel from the
> >> 64 bit xen build. After fixing up one or two minor issues with
> >> the elf loader, I believe I now have it to the point where it
> >> jumps correctly to the 32 bit kernel and it crashes there, since
> >> it is 32 bit code still executing on a cpu in 64 bit mode. The
> >> question is how to return the cpu to 32 bit mode *under xen*?
> >
> >
> > IIRC it was already discussed not long ago and it seems to be Xen
> > limitation. You probably need to ask on xen-devel to be sure.
> >
> > Is it not more simple to use 32 bit grub with 32 bit kernel to
> > start with?
>
> The problem with that is that you have to know in advance which kernel
> you are going to boot. That makes configuring virtual hosts harder;
> they just want one grub image they can use to chainload whatever the
> guest wants to install in their domain.
>
> Also there must be a way to do this otherwise a 64 bit kernel running
> under xen wouldn't be able to execute a 32 bit binary. I suppose I'll
> Cc xen-devel.
Running a 32-bit userspace under a 64-bit kernel is a very different
thing to switching a kernel from 64-bit down to 32-bit (or vice versa).
While the former is of course supported just fine the latter is not and
IIRC doing so would be very difficult for a PV kernel due to the way the
interfaces are constructed (e.g. to p2m entries change size, the maximum
addressable machine address changes).
Yes, this is a massive Pain In The A**.
Ian.
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^ permalink raw reply [flat|nested] 18+ messages in thread