Re: [Xen-ia64-devel] Re: [PATCH] Fix mca handler so as not to destroy ar

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Fri, Aug 08, 2008 at 03:41:17PM +0900, SUZUKI Kazuhiro wrote:

> I think gp passed from SAL is changed to a virtual address by
> DATA_PA_TO_VA() in VIRTUAL_MODE_ENTER().
> 
> #define DATA_PA_TO_VA(addr,temp)                      \
>       mov     temp    = 0xf   ;;                      \
>       dep     addr    = temp, addr, 60, 4
> 
> Could you please explain the issue a little more in detail?

The xen vmm image was made relocatable so that
xen text and data are located at the area starting at
        #define KERNEL_START             0xf400000004000000
wherever the image is loaded.
So __gp is a value of 0xf400000004000000 + offset
and it's impossible to calculate __gp from the physical address
of __gp.

On the other hand the macro, DATA_PA_TO_VA(), gives
a value of 0xf000000000000000 + physical address.
The value points to the same physical memory location pointed
by __gp, so possibly the current code may just work.
But it worried me much so that I checked the linux
code to find the c/s f5a3f3dc189485d607fbd42678cc23958acc0a6e.

Yes, it's easy for me (and you) to port the following hunk of the c/s,
however it's difficult for me to test the handler.

thanks,

diff --git a/include/asm-ia64/mca_asm.h b/include/asm-ia64/mca_asm.h
index 27c9203..76203f9 100644
--- a/include/asm-ia64/mca_asm.h
+++ b/include/asm-ia64/mca_asm.h
@@ -197,9 +197,9 @@
        movl    temp2 = start_addr;                             \
        ;;                                                      \
        mov     cr.iip = temp2;                                 \
+       movl    gp = __gp                                       \
        ;;                                                      \
        DATA_PA_TO_VA(sp, temp1);                               \
-       DATA_PA_TO_VA(gp, temp2);                               \
        srlz.i;                                                 \
        ;;                                                      \
        nop     1;                                              \


-- 
yamahata

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