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> >> + > >> + /* > >> + * When there's (supposedly) no RTC/CMOS, we don't intercept the other > >> + * ports. While reading the index register isn't normally possible, > >> + * play safe and return back whatever can be read (just in case a value > >> + * written through an alias would be attempted to be read back here). > >> + */ > >> + if ( port == RTC_PORT(0) && > >> + (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) && > >> + ioports_access_permitted(currd, port, port) ) > >> + data = inb(port) & 0x7f; > > > > Do we really need to mask the high bit here? We don't allow setting > > that bit in the first place. > > I think it's more consistent to mask it off, specifically with the code > visible in context right above the insertion. The doc isn't really clear > about readability of that bit: On one hand in says R/W for port 0x70 in > the NMI_EN section, yet otoh in the RTC section it says "Note that port > 70h is not directly readable. The only way to read this register is > through Alt Access mode." (I think the NMI_EN section is more trustworthy, > but still.) Plus if we were to ever make use of the NMI disable, we > wouldn't want Dom0 see the bit set. I guess so, at the end Xen itself doesn't use the bit so far. Maybe at some point we would want to expose the value of the bit to dom0 if Xen starts using it (most than anything for informative purposes if NMIs are disabled). Feel free to fold the diff to the existing patch and keep the RB. I guess you will also add something to the commit message about the special handling of the NMI enable bit even when the RTC/CMOS is not present? Thanks, Roger.