[Xen-devel] Re: [PATCH] X86 MCE: Add SRAR handler

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.10.11 at 22:25, "Liu, Jinsong" <jinsong.liu@xxxxxxxxx> wrote:
> I update a little for my former patch, as attached.
> For my former patch, you mainly have 2 concerns (list below). I double check 
> xen mce code, w/ my opinion append:

Those concerns were really just triggered by the patch, not directly
related to it. The patch itself looks okay to me.

> Concern 1: for SRAR IFU error, since RIPV=EIPV=0, it maybe an async error 
> which occur at guest but root from hypervisor.
> [Jinsong]: 
>     Yes, but EIPV didn't tell us where the error root from (it's just a 
> hint, warning us async possibility). 
>     It no need to overkill xen at mce isr, instead, at mce softirq we can 
> find out error root location and then handle accordingly:
>     * at mce isr:
>             /* a total insurance */
>             /* if error is async, we delay handle it at mce softirq */
>             if ( !(gstatus & MCG_STATUS_RIPV) && !guest_mode(regs))
>                 return -1;

I continue to think that guest_mode() must not be used without
EIPV, no matter what the purpose of the use.

>     * at mce softirq:
>             /* detect error location by bank->mc_addr */
>             /* handle different page OWNER cases at intel_memerr_dhandler() 
> and offline_page() */
>             /* who own, who take */
>             if (error page owner is guest)
>                 trigger vmce to guest;
>             else
>                 panic xen;

That part is certainly fine.

> Concern 2: If a guest accesses the hypervisor part of the GDT or page 
> tables, or some other shared data structure owned by the hypervisor (like the 
> M2P table), its handler may get utterly confused by being presented an 
> address it doesn't own and knows nothing about.
> [Jinsong]: for such cases, page owner would be dom_xen/dom_cow or NULL, but 
> not guest --> it would be handled at hypervisor, not triggering vmce to guest 
> --> 
> who own, who take.

That latter part of your explanation is fine too, but with the caveat that
the bogus use of guest_mode() above may have an overall effect on the
behavior.

Jan


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