On 02/09/2011 10:19, "Igor Mammedov" <imammedo@xxxxxxxxxx> wrote:
> BTW, while debugging this issue, I've tried to print saved_upcall_mask
> inside xen when handling page fault from guest. And it value is always
> 0. Looking at asm code for example in xen/arch/x86/x86_32/entry.S:382
>
> movzwl TRAPBOUNCE_cs(%edx),%eax 
> ^^^^^ upper 16-bit is 0 set in propagate_page_fault
> by "tb->cs = ti->cs;"
>
> /* Null selectors (0-3) are not allowed. */
> testl $~3,%eax
> jz domain_crash_synchronous
> movl %eax,UREGS_cs+4(%esp)
> ^^^^^^^^^^^^^^^^ and here is the only place we set
> saved_upcall_mask field in current cpu_user_regs
>
> It looks like "saved_upcall_mask" in cpu_user_regs is not really used
> any more for what it means and it's presence in struct is just confusing
> and misleading.
>
> So why not delete it and extend _pad1 to 4 bytes?
It's part of the guest ABI.
 -- Keir
>
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