linux-kernel - Re: [PATCH v2 12/12] KVM: arm64: BTI: Reset BTYPE when skipping emulated instructions

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Message-ID: <20191011144451.GI27757@arm.com>
Date:   Fri, 11 Oct 2019 15:44:51 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Amit Kachhap <amit.kachhap@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-arch@...r.kernel.org, Eugene Syromiatnikov <esyr@...hat.com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>, Andrew Jones <drjones@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Mark Brown <broonie@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        Florian Weimer <fweimer@...hat.com>,
        linux-kernel@...r.kernel.org, Sudakshina Das <sudi.das@....com>
Subject: Re: [PATCH v2 12/12] KVM: arm64: BTI: Reset BTYPE when skipping
 emulated instructions

On Fri, Oct 11, 2019 at 03:24:55PM +0100, Mark Rutland wrote:
> On Thu, Oct 10, 2019 at 07:44:40PM +0100, Dave Martin wrote:
> > Since normal execution of any non-branch instruction resets the
> > PSTATE BTYPE field to 0, so do the same thing when emulating a
> > trapped instruction.
> > 
> > Branches don't trap directly, so we should never need to assign a
> > non-zero value to BTYPE here.
> > 
> > Signed-off-by: Dave Martin <Dave.Martin@....com>
> > ---
> >  arch/arm64/include/asm/kvm_emulate.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index d69c1ef..33957a12 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> > @@ -452,8 +452,10 @@ static inline void kvm_skip_instr(struct kvm_vcpu *vcpu, bool is_wide_instr)
> >  {
> >  	if (vcpu_mode_is_32bit(vcpu))
> >  		kvm_skip_instr32(vcpu, is_wide_instr);
> > -	else
> > +	else {
> >  		*vcpu_pc(vcpu) += 4;
> > +		*vcpu_cpsr(vcpu) &= ~(u64)PSR_BTYPE_MASK;
> > +	}
> 
> Style nit: both sides of an if-else should match brace-wise. i.e. please
> add braces to the other side.

Will fix.  Strange, checkpatch didn't catch that, maybe because only one
arm of the if was patched.

> As with the prior patch, the u64 cast can also go.
> 
> Otherwise, this looks right to me.

For some reason I thought there was a different prevailing style in the
KVM code, but now I see no evidence of that.

Will fix.

Thanks for the review.

Cheers
---Dave