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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 3 Apr 2017, Julien Grall wrote:
> Hi Stefano,
> 
> On 31/03/17 23:33, Stefano Stabellini wrote:
> > 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.
> 
> Sorry, I was not clear. You assume that vwfi == TRAP by default, although I
> guess it is fine because it is a backport.

Yes, that was my thinking. See new patch:
alpine.DEB.2.10.1703311535180.3287@sstabellini-ThinkPad-X260

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