I have been
trying to trace how the system starts a HVM guest by reading HVM loader source
code for three days.. I still have many questions on running bios and HVM guest
kerenl. The follows are some of them.
I appreciate any
help on these.
Q1. After “call
main” in hvmloader.c in tools/firmware/hvmloader, the system jumps to
execute vmxassist.
In “setup_ctx()”
in vmxassist/setup.c, “switch_to_real_mode” is assigned to a newctxt c->eip.
How this newctxt is executed?
Q2. How does the
entering VM86 happen? The clue of entering VM86 seems broken after
enter_real_mode function.
Q3. After returning
from “call main” in tools/firmware/hvmloader/hvmloader.c, the system setups a real-mode
trampoline and move it to 0x0, then jmp to F000:FFF0. Is it to continue
executing HVM guest OS? If so, how is HVM guest loaded to such an address?
Q4. Is the
system in VMX root mode when setting-up the real-mode trampoline in Q3? If so
how does it deal with this kind of vmexit?
Best
regards,
Hu Jia
Yi
Ext:
20430
Tel:
65-67510430
-----Original Message-----
From: Keir Fraser
[mailto:Keir.Fraser@xxxxxxxxxxxx]
Sent: Thursday, February 28, 2008
5:52 PM
To: Hu Jia Yi; Cui, Dexuan;
xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] A
question on vmx loader in xen - how and when rombiosis loaded into memory
There
isn’t such a document. You can probably find a short list of bullet points on
xen.org. Yes emulation much slower but modern bootloaders spend only a short
time in real mode. The exceptions (e.g., SuSE bootloader pre-10.2) don’t work
with vm86 at all.
-- Keir
On 28/2/08 09:24, "Hu Jia Yi" <jyhu@xxxxxxxxx> wrote:
Where can I download documents elaborating the differences between
xen-3.2.0 and 3.1.0.
The white paper in xen.org is too short to be enlighting.
By the way, how can a full emulation of real mode be done? Is there a big speed
gap between the full emulation and VM86?
Best
regards,
Hu Jia Yi
Ext: 20430
Tel: 65-67510430
-----Original Message-----
From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
Sent: Thursday, February 28, 2008
4:59 PM
To: Hu Jia Yi; Cui, Dexuan;
xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] A
question on vmx loader in xen - how and when rombiosis loaded into memory
We don’t take that patch in Xen 3.2 and earlier. Instead
we use vmxassist (see the use_vmxassist() if statement immediately above the
jump to f000:fff0). In current xen-unstable we have got rid of vmxassist and
Xen itself does full emulation of real mode; and the tools/firmware/README is
gone!
-- Keir
On 28/2/08 07:33, "Hu Jia Yi" <jyhu@xxxxxxxxx> wrote:
Thank you.
I notice the system then jumps to F000:FFF0 to execute. But because VMX is
turned on, switching to real-mode would incur problems?
I don’t find any clue to turn on the vm86 mode as Readme in the tools/firmware
directory puts.
Best
regards,
Hu Jia Yi
Ext: 20430
Tel: 65-67510430
-----Original Message-----
From: Cui, Dexuan [mailto:dexuan.cui@xxxxxxxxx] <mailto:dexuan.cui@xxxxxxxxx%5d>
Sent: Thursday, February 28, 2008
11:43 AM
To: Hu Jia Yi;
xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: RE: [Xen-devel] A
question on vmx loader in xen - how and when rombiosis loaded into memory
> how and when rombios, vgabios and vmxassist have been
loaded to the memory from the disk before calling “memcpy”.
They are statically compiled into hvmloader in the way of
C array and are loaded with hvmloader.
Please step into the directory hvmloader/ and search for "roms.h" in
Makefile.
-- Dexuan
From:
xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx]
<mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx%5d>
On Behalf Of Hu Jia Yi
Sent: 2008年2月28日 11:26
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] A question on
vmx loader in xen - how and when rombiosis loaded into memory
A “main”
function is defined in Xen-3.1.0-source/tools/firmware/hvmloader/hvmloader.c.
In this main function, rombios, vgabios and vmxassist are copied to specified
address,
with following commands
memcpy((void *)ROMBIOS_PHYSICAL_ADDRESS,
rombios, rombios_sz);
…
memcpy((void *)ETHERBOOT_PHYSICAL_ADDRESS, etherboot, sizeof(etherboot));
….
But after searching the whole
directory “firmware”, I don’t know how and when rombios, vgabios and
vmxassist have been loaded to the memory from the disk before calling “memcpy”.
Could anybody help me on this?
Best
regards,
Hu Jia Yi
Ext: 20430
Tel: 65-67510430
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