Re: [Xen-devel] [PATCH v2] setup vwfi correctly on cpu0

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 3 Apr 2017, Julien Grall wrote:
> Hi Stefano,
> 
> On 03/31/2017 11:37 PM, Stefano Stabellini wrote:
> > parse_vwfi runs after init_traps on cpu0, potentially resulting in the
> > wrong HCR_EL2 for it. Secondary cpus boot after parse_vwfi, so in their
> > case init_traps will write the correct set of flags to HCR_EL2.
> > 
> > For cpu0, fix the issue by changing HCR_EL2 setting from a new
> > presmp_initcall.
> > 
> > Signed-off-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > 
> > ---
> > This patch should be apply to 4.8, 4.7, 4.6, not to unstable (it will be
> > fixed differently there).
> > ---
> > 
> > diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> > index 614501f..65b5397 100644
> > --- a/xen/arch/arm/traps.c
> > +++ b/xen/arch/arm/traps.c
> > @@ -115,6 +115,22 @@ static void __init parse_vwfi(const char *s)
> >  }
> >  custom_param("vwfi", parse_vwfi);
> > 
> > +static int __init vwfi_init(void)
> > +{
> > +    /*
> > +     * HCR_EL2 has already been set on cpu0, change the setting here, if
> > +     * needed. Other cpus haven't booted yet, init_traps will setup
> > +     * HCR_EL2 correctly.
> > +     */
> > +    if ( vwfi == NATIVE ) {
> 
> Coding style:
> 
> if ( ... )
> {
> 
> > +        register_t hcr;
> 
> NIT: newline here please.
> 
> 
> > +        hcr = READ_SYSREG(HCR_EL2);
> > +        WRITE_SYSREG(hcr & ~(HCR_TWI|HCR_TWE), HCR_EL2);
> > +    }
> 
> Ditto.
> 
> > +    return 0;
> > +}
> > +presmp_initcall(vwfi_init);
> > +
> >  void init_traps(void)
> >  {
> >      /* Setup Hyp vector base */
> > 
> 
> With that:
> 
> Reviewed-by: Julien Grall <julien.grall@xxxxxxx>

I committed the patch with your comments. However, because of the
backporting rules (only pushed-gated commits should be backported), I
only pushed it to staging for now.

I expect Wei Chen (CC'ed) to revert this patch completely or partially
as part of his series. Wei, to be clear, I committed this patch to fix a
bug on the stable trees where the vwfi option is not set correctly on
cpu0. With your series, this bug will be fixed in a much nicer way.

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