Messages in this thread | | | Date | Thu, 18 Jan 2007 13:30:03 +0530 | From | Vivek Goyal <> | Subject | Re: PATCH: Update disable_IO_APIC to use 8-bit destination field (X86_64) |
| |
On Thu, Jan 18, 2007 at 12:10:55AM -0700, Eric W. Biederman wrote: > Vivek Goyal <vgoyal@in.ibm.com> writes: > > > > Or how about making physical_dest field also 8bit like logical_dest field. > > This will work both for 4bit and 8bit physical apic ids at the same time > > code becomes more intutive and it is easier to know whether IOAPIC is being > > put in physical or destination logical mode. > > Exactly what I was trying to suggest. > > Looking closer at the code I think it makes sense to just kill the union and > stop the discrimination between physical and logical modes and just have a > dest field in the structure. Roughly as you were suggesting at first. > > The reason we aren't bitten by this on a regular basis is the normal code > path uses logical.logical_dest in both logical and physical modes. > Which is a little confusing. > > Since there really isn't a distinction to be made we should just stop > trying, which will make maintenance easier :) > > Currently there are several non-common case users of physical_dest > that are probably bitten by this problem under the right > circumstances. > > So I think we should just make the structure: > > struct IO_APIC_route_entry { > __u32 vector : 8, > delivery_mode : 3, /* 000: FIXED > * 001: lowest prio > * 111: ExtINT > */ > dest_mode : 1, /* 0: physical, 1: logical */ > delivery_status : 1, > polarity : 1, > irr : 1, > trigger : 1, /* 0: edge, 1: level */ > mask : 1, /* 0: enabled, 1: disabled */ > __reserved_2 : 15; > > __u32 __reserved_3 : 24, > __dest : 8; > } __attribute__ ((packed)); > > And fixup the users. This should keep us from getting bit by this bug > in the future. Like when people start introducing support for more > than 256 cores and the low 24bits start getting used. > > Or when someone new starts working on the code and thinks the fact > the field name says logical we are actually using the apic in logical > mode.
This makes perfect sense to me. Ben, interested in providing a patch for this?
Thanks Vivek - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |