Re: [PATCH] KVM: PPC: Book3S HV: Fix TLB management on SMT8 POWER9 and POWER10 processors

[Fabiano Rosas <farosas@linux.ibm.com>]

Nicholas Piggin <npiggin@gmail.com> writes:

> From: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
>
> The POWER9 vCPU TLB management code assumes all threads in a core share
> a TLB, and that TLBIEL execued by one thread will invalidate TLBs for
> all threads. This is not the case for SMT8 capable POWER9 and POWER10
> (big core) processors, where the TLB is split between groups of threads.
> This results in TLB multi-hits, random data corruption, etc.
>
> Fix this by introducing cpu_first_tlb_thread_sibling etc., to determine
> which siblings share TLBs, and use that in the guest TLB flushing code.
>
> [npiggin@gmail.com: add changelog and comment]
>
> Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>

> ---
>  arch/powerpc/include/asm/cputhreads.h | 30 +++++++++++++++++++++++++++
>  arch/powerpc/kvm/book3s_hv.c          | 13 ++++++------
>  arch/powerpc/kvm/book3s_hv_builtin.c  |  2 +-
>  arch/powerpc/kvm/book3s_hv_rm_mmu.c   |  2 +-
>  4 files changed, 39 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/cputhreads.h b/arch/powerpc/include/asm/cputhreads.h
> index 98c8bd155bf9..b167186aaee4 100644
> --- a/arch/powerpc/include/asm/cputhreads.h
> +++ b/arch/powerpc/include/asm/cputhreads.h
> @@ -98,6 +98,36 @@ static inline int cpu_last_thread_sibling(int cpu)
>  	return cpu | (threads_per_core - 1);
>  }
>
> +/*
> + * tlb_thread_siblings are siblings which share a TLB. This is not
> + * architected, is not something a hypervisor could emulate and a future
> + * CPU may change behaviour even in compat mode, so this should only be
> + * used on PowerNV, and only with care.
> + */
> +static inline int cpu_first_tlb_thread_sibling(int cpu)
> +{
> +	if (cpu_has_feature(CPU_FTR_ARCH_300) && (threads_per_core == 8))
> +		return cpu & ~0x6;	/* Big Core */
> +	else
> +		return cpu_first_thread_sibling(cpu);
> +}
> +
> +static inline int cpu_last_tlb_thread_sibling(int cpu)
> +{
> +	if (cpu_has_feature(CPU_FTR_ARCH_300) && (threads_per_core == 8))
> +		return cpu | 0x6;	/* Big Core */
> +	else
> +		return cpu_last_thread_sibling(cpu);
> +}
> +
> +static inline int cpu_tlb_thread_sibling_step(void)
> +{
> +	if (cpu_has_feature(CPU_FTR_ARCH_300) && (threads_per_core == 8))
> +		return 2;		/* Big Core */
> +	else
> +		return 1;
> +}
> +
>  static inline u32 get_tensr(void)
>  {
>  #ifdef	CONFIG_BOOKE
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 28a80d240b76..0a8398a63f80 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -2657,7 +2657,7 @@ static void radix_flush_cpu(struct kvm *kvm, int cpu, struct kvm_vcpu *vcpu)
>  	cpumask_t *cpu_in_guest;
>  	int i;
>
> -	cpu = cpu_first_thread_sibling(cpu);
> +	cpu = cpu_first_tlb_thread_sibling(cpu);
>  	if (nested) {
>  		cpumask_set_cpu(cpu, &nested->need_tlb_flush);
>  		cpu_in_guest = &nested->cpu_in_guest;
> @@ -2671,9 +2671,10 @@ static void radix_flush_cpu(struct kvm *kvm, int cpu, struct kvm_vcpu *vcpu)
>  	 * the other side is the first smp_mb() in kvmppc_run_core().
>  	 */
>  	smp_mb();
> -	for (i = 0; i < threads_per_core; ++i)
> -		if (cpumask_test_cpu(cpu + i, cpu_in_guest))
> -			smp_call_function_single(cpu + i, do_nothing, NULL, 1);
> +	for (i = cpu; i <= cpu_last_tlb_thread_sibling(cpu);
> +					i += cpu_tlb_thread_sibling_step())
> +		if (cpumask_test_cpu(i, cpu_in_guest))
> +			smp_call_function_single(i, do_nothing, NULL, 1);
>  }
>
>  static void kvmppc_prepare_radix_vcpu(struct kvm_vcpu *vcpu, int pcpu)
> @@ -2704,8 +2705,8 @@ static void kvmppc_prepare_radix_vcpu(struct kvm_vcpu *vcpu, int pcpu)
>  	 */
>  	if (prev_cpu != pcpu) {
>  		if (prev_cpu >= 0 &&
> -		    cpu_first_thread_sibling(prev_cpu) !=
> -		    cpu_first_thread_sibling(pcpu))
> +		    cpu_first_tlb_thread_sibling(prev_cpu) !=
> +		    cpu_first_tlb_thread_sibling(pcpu))
>  			radix_flush_cpu(kvm, prev_cpu, vcpu);
>  		if (nested)
>  			nested->prev_cpu[vcpu->arch.nested_vcpu_id] = pcpu;
> diff --git a/arch/powerpc/kvm/book3s_hv_builtin.c b/arch/powerpc/kvm/book3s_hv_builtin.c
> index 7a0e33a9c980..3edc25c89092 100644
> --- a/arch/powerpc/kvm/book3s_hv_builtin.c
> +++ b/arch/powerpc/kvm/book3s_hv_builtin.c
> @@ -800,7 +800,7 @@ void kvmppc_check_need_tlb_flush(struct kvm *kvm, int pcpu,
>  	 * Thus we make all 4 threads use the same bit.
>  	 */
>  	if (cpu_has_feature(CPU_FTR_ARCH_300))
> -		pcpu = cpu_first_thread_sibling(pcpu);
> +		pcpu = cpu_first_tlb_thread_sibling(pcpu);
>
>  	if (nested)
>  		need_tlb_flush = &nested->need_tlb_flush;
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 7af7c70f1468..407dbf21bcbc 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -67,7 +67,7 @@ static int global_invalidates(struct kvm *kvm)
>  		 * so use the bit for the first thread to represent the core.
>  		 */
>  		if (cpu_has_feature(CPU_FTR_ARCH_300))
> -			cpu = cpu_first_thread_sibling(cpu);
> +			cpu = cpu_first_tlb_thread_sibling(cpu);
>  		cpumask_clear_cpu(cpu, &kvm->arch.need_tlb_flush);
>  	}