lkml.org 
[lkml]   [2012]   [Apr]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Xen-devel] [PATCH] xen/apic: implement io apic read with hypercall
On 20/04/12 13:38, Ian Campbell wrote:
> On Fri, 2012-04-20 at 12:13 +0100, Lin Ming wrote:
>> On Fri, 2012-04-20 at 10:58 +0100, Andrew Cooper wrote:
>>> On 20/04/12 10:25, Lin Ming wrote:
>>>> Implements xen_io_apic_read with hypercall, so it returns proper IO-APIC
>>>> information instead of fabricated one.
>>>>
>>>> Signed-off-by: Lin Ming <mlin@ss.pku.edu.cn>
>>>> ---
>>>> arch/x86/xen/apic.c | 16 +++++++++++-----
>>>> 1 files changed, 11 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/x86/xen/apic.c b/arch/x86/xen/apic.c
>>>> index aee16ab..f1f392d 100644
>>>> --- a/arch/x86/xen/apic.c
>>>> +++ b/arch/x86/xen/apic.c
>>>> @@ -1,14 +1,20 @@
>>>> #include <linux/init.h>
>>>> #include <asm/x86_init.h>
>>>> +#include <asm/apic.h>
>>>> +#include <xen/interface/physdev.h>
>>>> +#include <asm/xen/hypercall.h>
>>>>
>>>> unsigned int xen_io_apic_read(unsigned apic, unsigned reg)
>>>> {
>>>> - if (reg == 0x1)
>>>> - return 0x00170020;
>>>> - else if (reg == 0x0)
>>>> - return apic << 24;
>>>> + struct physdev_apic apic_op;
>>>> + int ret;
>>>>
>>>> - return 0xff;
>>>> + apic_op.apic_physbase = mpc_ioapic_addr(apic);
>>>> + apic_op.reg = reg;
>>>> + ret = HYPERVISOR_physdev_op(PHYSDEVOP_apic_read, &apic_op);
>>>> + if (ret)
>>>> + return ret;
>>>> + return apic_op.value;
>>> Hypercall ret errors are negative, yet this function is unsigned. Given
>>> that the previous function had no possible way to fail, perhaps on error
>>> you should fake up the values as before.
>> How about return -1 on error?
>> The calling function can check -1 for error.
> Isn't -1 potentially (at least theoretically) a valid value to read from
> one of these registers?

Theoretically yes, but practically it would only be buggy hardware
returning -1.

>
> Under what circumstances can these hypercalls fail? Would a BUG_ON be
> appropriate/

-EFAULT, -EPERM, anything xsm_apic() could return (which looks only to
be -EPERM). The call into Xen itself will return 0 as a value if an
invalid physbase is passed in the hypercall.

So a BUG_ON() is not safe/sensible for domU.

>
>> unsigned int ret = apic_read(...);
>> if (ret == -1)
>> //handle error.
>>
>> Thanks,
>> Lin Ming
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@lists.xen.org
>> http://lists.xen.org/xen-devel
>

--
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com



\
 
 \ /
  Last update: 2012-04-20 14:55    [from the cache]
©2003-2011 Jasper Spaans