Subject: Re: [PATCH 3/3] powerpc: Avoid load hit store when using find_linux_pte_or_hugepte()

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 30 May 2016 10:47:33 +0530

Anton Blanchard <[email-masked]> writes:

> From: Anton Blanchard <[email-masked]>
>
> In many cases we disable interrupts right before calling
> find_linux_pte_or_hugepte().
>
> find_linux_pte_or_hugepte() first checks interrupts are disabled
> before calling __find_linux_pte_or_hugepte():
>
>         if (!arch_irqs_disabled()) {
>                 pr_info("%s called with irq enabled\n", __func__);
>                 dump_stack();
>         }
>         return __find_linux_pte_or_hugepte(pgdir, ea, is_thp, shift);
>
> We know interrupts are disabled, but since the arch_irqs_*() macros
> are hidden from the compiler with inline assembly, gcc does not. We
> end up with a pretty awful load hit store:
>
> 	li      r9,0
> 	lbz     r24,570(r13)
> 	stb     r9,570(r13)	<----
> 	lbz     r9,570(r13)	<---- ouch
> 	cmpdi   cr7,r9,0
> 	bne     cr7,c000000000049d30
>
> Find these cases, and call __find_linux_pte_or_hugepte() directly.
>

Reviewed-by: Aneesh Kumar K.V <[email-masked]>
> Signed-off-by: Anton Blanchard <[email-masked]>
> ---
>  arch/powerpc/kvm/book3s_64_mmu_hv.c | 2 +-
>  arch/powerpc/kvm/book3s_hv_rm_mmu.c | 2 +-
>  arch/powerpc/kvm/e500_mmu_host.c    | 2 +-
>  arch/powerpc/mm/hash_utils_64.c     | 2 +-
>  arch/powerpc/mm/hugetlbpage.c       | 2 +-
>  arch/powerpc/mm/tlb_hash64.c        | 5 +++--
>  arch/powerpc/perf/callchain.c       | 2 +-
>  7 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index 05f09ae..ff53db5 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -543,7 +543,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
>  			 * hugepage split and collapse.
>  			 */
>  			local_irq_save(flags);
> -			ptep = find_linux_pte_or_hugepte(current->mm->pgd,
> +			ptep = __find_linux_pte_or_hugepte(current->mm->pgd,
>  							 hva, NULL, NULL);
>  			if (ptep) {
>  				pte = kvmppc_read_update_linux_pte(ptep, 1);
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 99b4e9d..8ee1f49 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -225,7 +225,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
>  						   &hpage_shift);
>  	else {
>  		local_irq_save(irq_flags);
> -		ptep = find_linux_pte_or_hugepte(pgdir, hva, NULL,
> +		ptep = __find_linux_pte_or_hugepte(pgdir, hva, NULL,
>  						 &hpage_shift);
>  	}
>  	if (ptep) {
> diff --git a/arch/powerpc/kvm/e500_mmu_host.c b/arch/powerpc/kvm/e500_mmu_host.c
> index b0333cc..b6487f5 100644
> --- a/arch/powerpc/kvm/e500_mmu_host.c
> +++ b/arch/powerpc/kvm/e500_mmu_host.c
> @@ -476,7 +476,7 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500,
>  	 * can't run hence pfn won't change.
>  	 */
>  	local_irq_save(flags);
> -	ptep = find_linux_pte_or_hugepte(pgdir, hva, NULL, NULL);
> +	ptep = __find_linux_pte_or_hugepte(pgdir, hva, NULL, NULL);
>  	if (ptep) {
>  		pte_t pte = READ_ONCE(*ptep);
>
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 5926896..5e47caa 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -1384,7 +1384,7 @@ void hash_preload(struct mm_struct *mm, unsigned long ea,
>  	 * THP pages use update_mmu_cache_pmd. We don't do
>  	 * hash preload there. Hence can ignore THP here
>  	 */
> -	ptep = find_linux_pte_or_hugepte(pgdir, ea, NULL, &hugepage_shift);
> +	ptep = __find_linux_pte_or_hugepte(pgdir, ea, NULL, &hugepage_shift);
>  	if (!ptep)
>  		goto out_exit;
>
> diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
> index 5aac1a3..ee8bc5b 100644
> --- a/arch/powerpc/mm/hugetlbpage.c
> +++ b/arch/powerpc/mm/hugetlbpage.c
> @@ -637,7 +637,7 @@ follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
>  	struct page *page = ERR_PTR(-EINVAL);
>
>  	local_irq_save(flags);
> -	ptep = find_linux_pte_or_hugepte(mm->pgd, address, &is_thp, &shift);
> +	ptep = __find_linux_pte_or_hugepte(mm->pgd, address, &is_thp, &shift);
>  	if (!ptep)
>  		goto no_page;
>  	pte = READ_ONCE(*ptep);
> diff --git a/arch/powerpc/mm/tlb_hash64.c b/arch/powerpc/mm/tlb_hash64.c
> index 4517aa4..f41bf3d 100644
> --- a/arch/powerpc/mm/tlb_hash64.c
> +++ b/arch/powerpc/mm/tlb_hash64.c
> @@ -209,8 +209,9 @@ void __flush_hash_table_range(struct mm_struct *mm, unsigned long start,
>  	local_irq_save(flags);
>  	arch_enter_lazy_mmu_mode();
>  	for (; start < end; start += PAGE_SIZE) {
> -		pte_t *ptep = find_linux_pte_or_hugepte(mm->pgd, start, &is_thp,
> -							&hugepage_shift);
> +		pte_t *ptep = __find_linux_pte_or_hugepte(mm->pgd, start,
> +							  &is_thp,
> +							  &hugepage_shift);
>  		unsigned long pte;
>
>  		if (ptep == NULL)
> diff --git a/arch/powerpc/perf/callchain.c b/arch/powerpc/perf/callchain.c
> index 0fc2671..f4d1d88 100644
> --- a/arch/powerpc/perf/callchain.c
> +++ b/arch/powerpc/perf/callchain.c
> @@ -127,7 +127,7 @@ static int read_user_stack_slow(void __user *ptr, void *buf, int nb)
>  		return -EFAULT;
>
>  	local_irq_save(flags);
> -	ptep = find_linux_pte_or_hugepte(pgdir, addr, NULL, &shift);
> +	ptep = __find_linux_pte_or_hugepte(pgdir, addr, NULL, &shift);
>  	if (!ptep)
>  		goto err_out;
>  	if (!shift)
> -- 
> 2.7.4