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

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Date:   Fri, 26 Jul 2019 16:05:01 +0200
From:   Anders Roxell <anders.roxell@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: KVM: regmap: Mark expected switch fall-through

On Fri, 26 Jul 2019 at 14:30, Marc Zyngier <marc.zyngier@....com> wrote:
>
> 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?

I made two mistakes.
1. saying 3.x instead of 4.x
2. I said the same kernel that 'git describe' showed and not the later one.

I did not know about '--match='.

> 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

That's correct.

>
>
> > 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).

It should be v4.17+.

Cheers,
Anders