Re: [Xen-ia64-devel] PATCH [resend]: more case handled in mmio.c

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Jeudi 20 Avril 2006 06:28, Xu, Anthony a écrit :
> From: Tristan Gingold
>
> >Sent: 2006?4?18? 16:44
> >Correct, but this doesn't happen in the mmio case, because fp_reg_disabled
> > is tested before doing the memory access.
>
> I didn't find where fp_reg_disabled is tested:-)
The processor does it.

> If we only emulate stf.spill and stf8, yes fp fault doesn't happen.
Yes.

> But if we need to emulate ldf, definitely fp fault will happen,
Yes, but in this case we don't call vcpu_get_fpreg!

> The sequence of emulating ldf maybe,
> Mmio_access( , , , , ,IOREQ_READ)
> Vcpu_set_fpreg( )
> Mmio_access will cause domain_switch,
> When switch back, psr.dfh is set,
> Then when executing vcpu_set_fpreg, fp fault happens.
>
> And I had found Xwindow use ldfp8 instruction to access frame buffer.
> BTW, Where did you find stf.spill and stf8 are used to access mmio?
memset.

> Can we address this issue like below?
> #ifdef        XEN
> #define ia64_fph_enable()
> #define ia64_fph_disable()
> #else
> #define ia64_fph_enable()     do { ia64_rsm(IA64_PSR_DFH); ia64_srlz_d(); }
> while (0) #define ia64_fph_disable()  do { ia64_ssm(IA64_PSR_DFH);
> ia64_srlz_d(); } while (0) #endif //XEN
>
> This makes sure there is no fp fault happening within xen.
I am quiet sure we need the ia64_fph_enable before saving fp regs!

> Yes later on if we want to use lazy fp algorithm within xen,
> we should revisit this.
Sure.

Thanks,
Tristan.



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