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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 31 Mar 2017, Julien Grall wrote:
> Hi Stefano,
> 
> On 03/30/2017 11:35 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 directly in
> > parse_vwfi.
> > 
> > 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..94d2e8a 100644
> > --- a/xen/arch/arm/traps.c
> > +++ b/xen/arch/arm/traps.c
> > @@ -112,6 +112,16 @@ static void __init parse_vwfi(const char *s)
> >             vwfi = NATIVE;
> >     else
> >             vwfi = TRAP;
> > +    /*
> > +     * 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 ( ... )
> {

OK


> > +        register_t hcr;
> > +        hcr = READ_SYSREG(HCR_EL2);
> > +        WRITE_SYSREG(hcr & ~(HCR_TWI|HCR_TWE), HCR_EL2);
> 
> You are assuming the default value of vwfi and it makes very complicate for
> someone to follow the code and modify it.

Do you mean the default vwfi setting? If so, no, I am not: hcr &
~(HCR_TWI|HCR_TWE) works regardless of the default.


> IHMO, a parsing function should only parse the command line and setup
> variable. Hardware configuration or initialization should be done separately
> (such as in an init call).

That is true. Given that this is meant for backports I was rewarding
shortness over cleanliness. I'll introduce a presmp_initcall, should
still be short enough.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel