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

From: "Nicholas Piggin" <[email-masked]>
Date: Mon, 15 May 2023 15:53:49 +1000

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 <[email-masked]>

What's the go with accesses in asm? Does it just assume you know
what you're doing?

Reviewed-by: Nicholas Piggin <[email-masked]>

> ---
> 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