On Tue, Feb 07, 2017 at 06:17:10PM +1100, Alexey Kardashevskiy wrote:
> VFIO on sPAPR already implements guest memory pre-registration
> when the entire guest RAM gets pinned. This can be used to translate
> the physical address of a guest page containing the TCE list
> from H_PUT_TCE_INDIRECT.
> 
> This makes use of the pre-registrered memory API to access TCE list
> pages in order to avoid unnecessary locking on the KVM memory
> reverse map as we know that all of guest memory is pinned and
> we have a flat array mapping GPA to HPA which makes it simpler and
> quicker to index into that array (even with looking up the
> kernel page tables in vmalloc_to_phys) than it is to find the memslot,
> lock the rmap entry, look up the user page tables, and unlock the rmap
> entry. Note that the rmap pointer is initialized to NULL
> where declared (not in this patch).
> 
> If a requested chunk of memory has not been preregistered, this will
> fall back to non-preregistered case and lock rmap.
> 
> Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>

Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>

> ---
> Changes:
> v4:
> * removed oneline inlines
> * now falls back to locking rmap if TCE list is not in preregistered memory
> 
> v2:
> * updated the commit log with David's comment
> ---
>  arch/powerpc/kvm/book3s_64_vio_hv.c | 58 
> +++++++++++++++++++++++++++----------
>  1 file changed, 42 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c 
> b/arch/powerpc/kvm/book3s_64_vio_hv.c
> index f8a54b7c788e..dc1c66fda941 100644
> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> @@ -239,6 +239,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>       long i, ret = H_SUCCESS;
>       unsigned long tces, entry, tce, ua = 0;
>       unsigned long *rmap = NULL;
> +     bool prereg = false;
>  
>       stt = kvmppc_find_table(vcpu->kvm, liobn);
>       if (!stt)
> @@ -259,23 +260,47 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>       if (ret != H_SUCCESS)
>               return ret;
>  
> -     if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, &rmap))
> -             return H_TOO_HARD;
> +     if (mm_iommu_preregistered(vcpu->kvm->mm)) {
> +             /*
> +              * We get here if guest memory was pre-registered which
> +              * is normally VFIO case and gpa->hpa translation does not
> +              * depend on hpt.
> +              */
> +             struct mm_iommu_table_group_mem_t *mem;
>  
> -     rmap = (void *) vmalloc_to_phys(rmap);
> +             if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, NULL))
> +                     return H_TOO_HARD;
>  
> -     /*
> -      * Synchronize with the MMU notifier callbacks in
> -      * book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.).
> -      * While we have the rmap lock, code running on other CPUs
> -      * cannot finish unmapping the host real page that backs
> -      * this guest real page, so we are OK to access the host
> -      * real page.
> -      */
> -     lock_rmap(rmap);
> -     if (kvmppc_rm_ua_to_hpa(vcpu, ua, &tces)) {
> -             ret = H_TOO_HARD;
> -             goto unlock_exit;
> +             mem = mm_iommu_lookup_rm(vcpu->kvm->mm, ua, IOMMU_PAGE_SIZE_4K);
> +             if (mem)
> +                     prereg = mm_iommu_ua_to_hpa_rm(mem, ua, &tces) == 0;
> +     }
> +
> +     if (!prereg) {
> +             /*
> +              * This is usually a case of a guest with emulated devices only
> +              * when TCE list is not in preregistered memory.
> +              * We do not require memory to be preregistered in this case
> +              * so lock rmap and do __find_linux_pte_or_hugepte().
> +              */
> +             if (kvmppc_gpa_to_ua(vcpu->kvm, tce_list, &ua, &rmap))
> +                     return H_TOO_HARD;
> +
> +             rmap = (void *) vmalloc_to_phys(rmap);
> +
> +             /*
> +              * Synchronize with the MMU notifier callbacks in
> +              * book3s_64_mmu_hv.c (kvm_unmap_hva_hv etc.).
> +              * While we have the rmap lock, code running on other CPUs
> +              * cannot finish unmapping the host real page that backs
> +              * this guest real page, so we are OK to access the host
> +              * real page.
> +              */
> +             lock_rmap(rmap);
> +             if (kvmppc_rm_ua_to_hpa(vcpu, ua, &tces)) {
> +                     ret = H_TOO_HARD;
> +                     goto unlock_exit;
> +             }
>       }
>  
>       for (i = 0; i < npages; ++i) {
> @@ -293,7 +318,8 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>       }
>  
>  unlock_exit:
> -     unlock_rmap(rmap);
> +     if (rmap)
> +             unlock_rmap(rmap);
>  
>       return ret;
>  }

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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