Re: Hypercall from HVM guest

[Steve Ofsthun <sofsthun@virtualiron.com>]

Emre Can Sezer wrote:
> Hi,
> 
> I'm trying to communicate some information from an HVM guest to Xen. 
> Passing a pointer to a buffer would suffice and the communication will be
> single sided.  What is the best way to do this?
> 
> I've looked into making a hypercall from an HVM guest and came across this
> post on this mailing list by Steve Ofsthun:
> 
> http://lists.xensource.com/archives/html/xen-devel/2006-04/msg00526.html

This code is quite old and much has changed since then.  You should probably use the pv on hvm driver code as an example these days (xen/unmodified_drivers/linux-2.6/platform-pci).

What hypercalls are you trying to use?  Note that HVM guests are restricted to a subset of the normal PV guest hypercalls.

Steve

> 
> However, I'm unable to get this code to work.  I'm running a 64-bit system
> with the linux-2.6.26 kernel downloaded from kernel.org on top of
> xen-3.2.2.  When I compile, I get compilation errors resulting from
> hypercall.h.  I believe this code is intended for 32 bit guests only as
> the structure definitions are different fot the pte_t type.
> 
> The error was:
> In file included from include/asm/xen/hypervisor.h:53,
>                  from /home/ecsezer/kernels/vmcall/./features.c:11:
> include/asm/xen/hypercall.h: In function 'HYPERVISOR_update_va_mapping':
> include/asm/xen/hypercall.h:230: error: 'pte_t' has no member named 'pte_low'
> 
> I tried to modify this code to get rid of compilation errors but a final
> warning still persists and loading the module causes a seg fault.  The
> warning I get is:
>   CC [M]  /home/ecsezer/kernels/hyper/./hypercall.o
> {standard input}: Assembler messages:
> {standard input}:149: Warning: indirect call without `*'
> 
> So I tried to compile with mercurial repository version linux-2.6.18-xen
> and that compiles fine.  However, due to being a different version, I
> can't use the resulting module.
> 
> I would appreciate any insight as to how to proceed.  What could be the
> problem?  Perhaps there is an easier way of passing the information I want
> without a full blown hypercall interface?
> 
> Thanks,
> 
> John
> 
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