Re: [Xen-devel] [PATCH] 2/3: MCA/MCE correctable error handling

["Christoph Egger" <Christoph.Egger@xxxxxxx>]

I fixed all this in my code and will re-submit the new patch.

Christoph



On Wednesday 22 August 2007 12:01:26 Jan Beulich wrote:
> >>> "Christoph Egger" <Christoph.Egger@xxxxxxx> 22.08.07 10:47 >>>
> >
> >On Tuesday 21 August 2007 17:53:45 Jan Beulich wrote:
> >> >+} __attribute__((packed));
> >>
> >> I think it was a general agreement that it is not a good idea
> >> (non-portable to non-GNU compilers) to put things like this in public
> >> headers. I think by properly ordering things you can get away without
> >> this (and almost without padding).
> >
> >Oh, you're right. I should use #pragma pack(1)  instead.
> >Is this fine with you?
>
> I'm afraid that wouldn't work with the compat mode header generation, as
> the original use of #pragma pack(push, ...) was banned for (Sun)
> compatibility reasons. Consequently, I believe the only way of doing this
> properly is to avoid depending on compiler behavior by arranging things
> appropriately (including padding members if needed) and avoiding #pragma
> pack() altogether.
>
> >> >+struct mcinfo_global {
> >> >...
> >> >+    uint16_t mc_socketid;
> >> >+    uint16_t mc_coreid;
> >> >+    uint16_t mc_vcpu_id;
> >>
> >> Unless mc_vcpu_id is intended for that purpose, this neglects
> >> hyperthreading (I know, AMD doesn't use this, but the interface should
> >> be vendor neutral).
> >>
> >> If mc_vcpu_id is meant for that purpose, its naming is ambiguous.
> >>
> >> If mc_vcpu_id is meant as a vcpuid, then ordering things os that
> >> mc_domid and mc_vcpu_id are contiguous would seem more natural (making
> >> eventual examination in raw memory less confusing).
> >
> >mc_coreid is the physical core that reported the machine check
> > information. mc_socketid is the physical socket the physical core is in.
> > This is useful to find all other affected physical cores, when an error
> > in the L3-Cache is reported that is shared over all cores in the chip.
> >
> >mc_vcpu_id is the id of the active vcpu for the domain, that reported the
> >machine check information. Inside Xen, this is current->vcpu_id.
> >mc_vcpu_id is needed to deal properly with the upcoming NUMA support
> >my collegue is working on.
>
> Okay, but then you're really lacking a thread id here, for being filled by
> respective Intel code (AMD code would set this to zero).
>
> >> >+/* sizeof(struct mcinfo_global) + 6 * sizeof(struct mcinfo_bank) ==
> >> > 200. + * This is enough space to store mc information of up to six
> >> > banks. + */
> >> >+#define MCINFO_MAXSIZE (204 - sizeof(uint32_t))
> >>
> >> Why don't you use the sizeof()-s from the description? If this is really
> >> needed for some reason, then having 200 in the description and 204 in
> >> the macro is at least confusing...
> >
> >MCINFO_MAXSIZE is the size for the content of the mi_data array.
> >MCINFO_MAXSIZE + sizeof(mi_nentries) == 204. That is where is number comes
> >from.
>
> I concluded that, but pointed out that seeing two different numbers made
> me think of why this is so, whereas identical numbers would have avoided
> that (and will likely keep others from asking later, too).
>
> Also, you don't say what was the reason for you to use constants instead
> of sizeof() here.
>
> >> >     /* Frame containing list of mfns containing list of mfns
> >> > containing p2m. */ xen_pfn_t     pfn_to_mfn_frame_list_list;
> >> >     unsigned long nmi_reason;
> >> >+    struct arch_mc_info mc_info; /* machine check information */
> >> >     uint64_t pad[32];
> >> > };
> >>
> >> Are you sure it is appropriate to add a member here without reducing the
> >> padding member?
> >
> >You want me to replace "uint64_t pad[32];" with "uint32_t pad[13];" ?
>
> It would be my understanding that that's the right thing to do (assuming
> you calculated the numbers correctly), but I'd rely on Keir to give a final
> word on this.
>
> Jan



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