RE: [PATCH v5 20/34] x86/fred: add a machine check entry stub for FRED

Li, Xin3
2023-03-21T16:39:11Z

> On Tue, Mar 21, 2023 at 12:04:47AM +0000, Li, Xin3 wrote:
> > > > Unlike IDT, no need to save/restore dr7 in FRED machine check handler.
> > >
> > > Given how fragile MCE is, the question should be, do we ever want hw
> > > breakpoints to happen while it is running?
> >
> > HW breakpoints still work if they are properly configured.
> >
> > > If the hw-breakpoint handler trips on the same memory fail that got
> > > us into the mce the first time, we're dead.
> >
> > Right.
> >
> > Unless the MCIP bit is turned off any subsequent #MC goes to shutdown
> > ("machine is screwed").
> >
> > It's the kernel debugger's responsibility to decide how to proceed in
> > such cases. But if the kernel debugger itself is in a screwed memory
> > region, we are soooooo dead.
>
> Yeah, so I would much prefer, for robustness sake, to start out with not allowing
> #DB in MCE -- much like today.

Will disable #DB inside #MCE then.