[PATCH v2 08/11] powerpc: Mark writes registering ipi to host cpu through kvm and polling

[Rohan McLure]

> On 15 May 2023, at 3:53 pm, Nicholas Piggin <npiggin at gmail.com> wrote:
> 
> On Wed May 10, 2023 at 1:31 PM AEST, Rohan McLure wrote:
>> Mark writes to hypervisor ipi state so that KCSAN recognises these
>> asynchronous issue of kvmppc_{set,clear}_host_ipi to be intended, with
>> atomic writes. Mark asynchronous polls to this variable in
>> kvm_ppc_read_one_intr().
>> 
>> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> 
> What's the go with accesses in asm? Does it just assume you know
> what you're doing?

Exactly, KCSAN only emits instrumentation calls to around load/store 
instructions that the compiler itself generated. So by default, asm
accesses are not instrumented.

Thanks

> 
> Reviewed-by: Nicholas Piggin <npiggin at gmail.com>
> 
>> ---
>> v2: Add read-side annotations to both polling locations in
>> kvm_ppc_read_one_intr().
>> ---
>> arch/powerpc/include/asm/kvm_ppc.h   | 4 ++--
>> arch/powerpc/kvm/book3s_hv_builtin.c | 4 ++--
>> 2 files changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
>> index bc57d058ad5b..d701df006c08 100644
>> --- a/arch/powerpc/include/asm/kvm_ppc.h
>> +++ b/arch/powerpc/include/asm/kvm_ppc.h
>> @@ -548,12 +548,12 @@ static inline void kvmppc_set_host_ipi(int cpu)
>> * pairs with the barrier in kvmppc_clear_host_ipi()
>> */
>> smp_mb();
>> - paca_ptrs[cpu]->kvm_hstate.host_ipi = 1;
>> + WRITE_ONCE(paca_ptrs[cpu]->kvm_hstate.host_ipi, 1);
>> }
>> 
>> static inline void kvmppc_clear_host_ipi(int cpu)
>> {
>> - paca_ptrs[cpu]->kvm_hstate.host_ipi = 0;
>> + WRITE_ONCE(paca_ptrs[cpu]->kvm_hstate.host_ipi, 0);
>> /*
>> * order clearing of host_ipi flag vs. processing of IPI messages
>> *
>> diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
>> index da85f046377a..0f5b021fa559 100644
>> --- a/arch/powerpc/kvm/book3s_hv_builtin.c
>> +++ b/arch/powerpc/kvm/book3s_hv_builtin.c
>> @@ -406,7 +406,7 @@ static long kvmppc_read_one_intr(bool *again)
>> return 1;
>> 
>> /* see if a host IPI is pending */
>> - host_ipi = local_paca->kvm_hstate.host_ipi;
>> + host_ipi = READ_ONCE(local_paca->kvm_hstate.host_ipi);
>> if (host_ipi)
>> return 1;
>> 
>> @@ -466,7 +466,7 @@ static long kvmppc_read_one_intr(bool *again)
>> * meantime. If it's clear, we bounce the interrupt to the
>> * guest
>> */
>> - host_ipi = local_paca->kvm_hstate.host_ipi;
>> + host_ipi = READ_ONCE(local_paca->kvm_hstate.host_ipi);
>> if (unlikely(host_ipi != 0)) {
>> /* We raced with the host,
>> * we need to resend that IPI, bummer
>> -- 
>> 2.37.2
>