[Xen-devel] anomaly in irq check in fixup_page_fault()

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

Hi,

This is a bit confusing. This for PVOPs kernel, I've not looked at older
PV kernels to see what they do yet. But, the VCPU starts with 
evtchn_upcall_mask set and eflags.IF enabled. However, during kernel
boot memory mapping lot of faults are getting fixed up by xen in: 

fixup_page_fault():
    /* No fixups in interrupt context or when interrupts are disabled. */
    if ( in_irq() || !(regs->eflags & X86_EFLAGS_IF) )  <------
        return 0;

The guest is running under the assumption of INTs disabled during 
init_memory_mapping, and the first enable happens much later. So this
check seems redundant at least for PVOPs kernel.

Now for my hybrid, the guest during initial boot is running with IF 
disabled, so fixup doesn't like that. Not sure if permanently disabling
the (eflags & X86_EFLAGS_IF) check for hybrid would be a good idea for
me.

thanks,
Mukesh


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