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

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Message-ID: <20191011142454.GD33537@lakrids.cambridge.arm.com>
Date:   Fri, 11 Oct 2019 15:24:55 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-kernel@...r.kernel.org, Andrew Jones <drjones@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Kristina Martšenko <kristina.martsenko@....com>,
        Mark Brown <broonie@...nel.org>,
        Paul Elliott <paul.elliott@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Sudakshina Das <sudi.das@....com>,
        Szabolcs Nagy <szabolcs.nagy@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 12/12] KVM: arm64: BTI: Reset BTYPE when skipping
 emulated instructions

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.

As with the prior patch, the u64 cast can also go.

Otherwise, this looks right to me.

Thanks,
Mark.