linux-kernel - Re: [PATCH 1/2] arm64: KVM: regmap: Mark expected switch fall-through

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Date:   Fri, 26 Jul 2019 13:30:44 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: KVM: regmap: Mark expected switch fall-through

Hi Anders,

On Fri, 26 Jul 2019 12:27:05 +0100,
Anders Roxell <anders.roxell@...aro.org> wrote:
> 
> When fall-through warnings was enabled by default, commit d93512ef0f0e
> ("Makefile: Globally enable fall-through warning"), the following
> warnings was starting to show up:
> 
> In file included from ../arch/arm64/include/asm/kvm_emulate.h:19,
>                  from ../arch/arm64/kvm/regmap.c:13:
> ../arch/arm64/kvm/regmap.c: In function ‘vcpu_write_spsr32’:
> ../arch/arm64/include/asm/kvm_hyp.h:31:3: warning: this statement may fall
>  through [-Wimplicit-fallthrough=]
>    asm volatile(ALTERNATIVE(__msr_s(r##nvh, "%x0"), \
>    ^~~
> ../arch/arm64/include/asm/kvm_hyp.h:46:31: note: in expansion of macro ‘write_sysreg_elx’
>  #define write_sysreg_el1(v,r) write_sysreg_elx(v, r, _EL1, _EL12)
>                                ^~~~~~~~~~~~~~~~
> ../arch/arm64/kvm/regmap.c:180:3: note: in expansion of macro ‘write_sysreg_el1’
>    write_sysreg_el1(v, SYS_SPSR);
>    ^~~~~~~~~~~~~~~~
> ../arch/arm64/kvm/regmap.c:181:2: note: here
>   case KVM_SPSR_ABT:
>   ^~~~
> In file included from ../arch/arm64/include/asm/cputype.h:132,
>                  from ../arch/arm64/include/asm/cache.h:8,
>                  from ../include/linux/cache.h:6,
>                  from ../include/linux/printk.h:9,
>                  from ../include/linux/kernel.h:15,
>                  from ../include/asm-generic/bug.h:18,
>                  from ../arch/arm64/include/asm/bug.h:26,
>                  from ../include/linux/bug.h:5,
>                  from ../include/linux/mmdebug.h:5,
>                  from ../include/linux/mm.h:9,
>                  from ../arch/arm64/kvm/regmap.c:11:
> ../arch/arm64/include/asm/sysreg.h:837:2: warning: this statement may fall
>  through [-Wimplicit-fallthrough=]
>   asm volatile("msr " __stringify(r) ", %x0"  \
>   ^~~
> ../arch/arm64/kvm/regmap.c:182:3: note: in expansion of macro ‘write_sysreg’
>    write_sysreg(v, spsr_abt);
>    ^~~~~~~~~~~~
> ../arch/arm64/kvm/regmap.c:183:2: note: here
>   case KVM_SPSR_UND:
>   ^~~~
> 
> Rework to add a 'break;' in the swich-case since it didn't have that.
> That also made the compiler happy and didn't warn about fall-through.
> 
> Cc: stable@...r.kernel.org # v3.16+

Erm... Are you sure about that? Here's what I have:

$ git describe --contains  a892819560c4
kvm-arm-for-v4.17~44
$ git describe --contains --match='v*' a892819560c4
v4.17-rc1~72^2~36^2~44


> Fixes: a892819560c4 ("KVM: arm64: Prepare to handle deferred save/restore of 32-bit registers")
> Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> ---
>  arch/arm64/kvm/regmap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/arm64/kvm/regmap.c b/arch/arm64/kvm/regmap.c
> index 0d60e4f0af66..a900181e3867 100644
> --- a/arch/arm64/kvm/regmap.c
> +++ b/arch/arm64/kvm/regmap.c
> @@ -178,13 +178,18 @@ void vcpu_write_spsr32(struct kvm_vcpu *vcpu, unsigned long v)
>  	switch (spsr_idx) {
>  	case KVM_SPSR_SVC:
>  		write_sysreg_el1(v, SYS_SPSR);
> +		break;
>  	case KVM_SPSR_ABT:
>  		write_sysreg(v, spsr_abt);
> +		break;
>  	case KVM_SPSR_UND:
>  		write_sysreg(v, spsr_und);
> +		break;
>  	case KVM_SPSR_IRQ:
>  		write_sysreg(v, spsr_irq);
> +		break;
>  	case KVM_SPSR_FIQ:
>  		write_sysreg(v, spsr_fiq);
> +		break;
>  	}
>  }

Otherwise looks like the right fix to me. Let me know what you think
about the Fixes: tag (no need to resend for that).

Thanks,

	M.

-- 
Jazz is not dead, it just smells funny.