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Re: [Xen-devel] [PATCH v2] xen: x86_32: do not enable iterrupts when returning from exception in interrupt context

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?

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