Re: [PATCH 01/14] KVM: arm64: Provide the host_stage2_try() helper macro

[Fuad Tabba <tabba@google.com>]

Hi Quentin,

On Mon, Jul 19, 2021 at 11:47 AM Quentin Perret <qperret@google.com> wrote:
>
> We currently unmap all MMIO mappings from the host stage-2 to recycle
> the pages whenever we run out. In order to make this pattern easy to
> re-use from other places, factor the logic out into a dedicated macro.
> While at it, apply the macro for the kvm_pgtable_stage2_set_owner()
> calls. They're currently only called early on and are guaranteed to
> succeed, but making them robust to the -ENOMEM case doesn't hurt and
> will avoid painful debugging sessions later on.
>
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c | 38 ++++++++++++++-------------
>  1 file changed, 20 insertions(+), 18 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index d938ce95d3bd..56f2117c877b 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -208,6 +208,23 @@ static inline int __host_stage2_idmap(u64 start, u64 end,
>                                       prot, &host_s2_pool);
>  }
>
> +/*
> + * The pool has been provided with enough pages to cover all of memory with
> + * page granularity, but it is difficult to know how much of the MMIO range
> + * we will need to cover upfront, so we may need to 'recycle' the pages if we
> + * run out.
> + */
> +#define host_stage2_try(fn, ...)                                       \
> +       ({                                                              \
> +               int __ret = fn(__VA_ARGS__);                            \
> +               if (__ret == -ENOMEM) {                                 \
> +                       __ret = host_stage2_unmap_dev_all();            \
> +                       if (!__ret)                                     \
> +                               __ret = fn(__VA_ARGS__);                \
> +               }                                                       \
> +               __ret;                                                  \
> +        })

I think it might be good to document that this macro expects the
host_kvm.lock to be held.

Thanks,
/fuad

>  static int host_stage2_idmap(u64 addr)
>  {
>         enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W;
> @@ -223,22 +240,7 @@ static int host_stage2_idmap(u64 addr)
>         if (ret)
>                 goto unlock;
>
> -       ret = __host_stage2_idmap(range.start, range.end, prot);
> -       if (ret != -ENOMEM)
> -               goto unlock;
> -
> -       /*
> -        * The pool has been provided with enough pages to cover all of memory
> -        * with page granularity, but it is difficult to know how much of the
> -        * MMIO range we will need to cover upfront, so we may need to 'recycle'
> -        * the pages if we run out.
> -        */
> -       ret = host_stage2_unmap_dev_all();
> -       if (ret)
> -               goto unlock;
> -
> -       ret = __host_stage2_idmap(range.start, range.end, prot);
> -
> +       ret = host_stage2_try(__host_stage2_idmap, range.start, range.end, prot);
>  unlock:
>         hyp_spin_unlock(&host_kvm.lock);
>
> @@ -257,8 +259,8 @@ int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end)
>                 return -EINVAL;
>
>         hyp_spin_lock(&host_kvm.lock);
> -       ret = kvm_pgtable_stage2_set_owner(&host_kvm.pgt, start, end - start,
> -                                          &host_s2_pool, pkvm_hyp_id);
> +       ret = host_stage2_try(kvm_pgtable_stage2_set_owner, &host_kvm.pgt,
> +                             start, end - start, &host_s2_pool, pkvm_hyp_id);
>         hyp_spin_unlock(&host_kvm.lock);
>
>         return ret != -EAGAIN ? ret : 0;
> --
> 2.32.0.402.g57bb445576-goog
>