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    SubjectRe: [PATCH 7/8] x86/apic: Make cpu_mask_to_apicid() operations return error code
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    On Thu, 2012-06-07 at 15:15 +0200, Alexander Gordeev wrote:
    > Current cpu_mask_to_apicid() and cpu_mask_to_apicid_and()
    > implementations have few shortcomings:
    >
    > 1. A value returned by cpu_mask_to_apicid() is written to hardware
    > registers unconditionally. Should BAD_APICID get ever returned it will
    > be written to a hardware too. But the value of BAD_APICID is not
    > universal across all hardware in all modes and might cause unexpected
    > results, i.e. interrupts might get routed to CPUs that are not
    > configured to receive it.
    >
    > 2. Because the value of BAD_APICID is not universal it is counter-
    > intuitive to return it for a hardware where it does not make sense
    > (i.e. x2apic).
    >
    > 3. cpu_mask_to_apicid_and() operation is thought as an complement to
    > cpu_mask_to_apicid() that only applies a AND mask on top of a cpumask
    > being passed. Yet, as consequence of 18374d8 commit the two operations
    > are inconsistent in that of:
    > cpu_mask_to_apicid() should not get a offline CPU with the cpumask
    > cpu_mask_to_apicid_and() should not fail and return BAD_APICID
    > These limitations are impossible to realize just from looking at the
    > operations prototypes.
    >
    > Most of these shortcomings are resolved by returning a error code
    > instead of BAD_APICID. As the result, faults are reported back early
    > rather than possibilities to cause a unexpected behaviour exist (in case
    > of [1]).
    >
    > The only exception is setup_timer_IRQ0_pin() routine. Although obviously
    > controversial to this fix, its existing behaviour is preserved to not
    > break the fragile check_timer() and would better addressed in a separate
    > fix.
    >

    I am ok with these changes. But even better would be to remove the
    cpu_mask_to_apicid() and just use cpu_mask_to_apicid_and() instead.

    Looks like there are only two places cpu_mask_to_apicid() being used
    anyways. So instead of patches 7 and 8, can you remove
    cpu_mask_to_apicid() in patch-7 and fixup the return value of
    cpu_mask_to_apicid_and() in patch-8

    thanks,
    suresh



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