Re: [PATCH v3 03/21] KVM: arm64: Provide the host_stage2_try() helper macro

Fuad Tabba
2021-08-02T09:37:23Z

Hi Quentin.

On Thu, Jul 29, 2021 at 3:28 PM 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 | 40 +++++++++++++++------------
> 1 file changed, 22 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..74280a753efb 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -208,6 +208,25 @@ 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.
> + */

The comment you added in V2 about host_kvm.lock got dropped in favor
asserting that the lock is held.

Reviewed-by: Fuad Tabba <tabba@google.com>

Thanks,
/fuad

> +#define host_stage2_try(fn, ...) \
> + ({ \
> + int __ret; \
> + hyp_assert_lock_held(&host_kvm.lock); \
> + __ret = fn(__VA_ARGS__); \
> + if (__ret == -ENOMEM) { \
> + __ret = host_stage2_unmap_dev_all(); \
> + if (!__ret) \
> + __ret = fn(__VA_ARGS__); \
> + } \
> + __ret; \
> + })
> +
> static int host_stage2_idmap(u64 addr)
> {
> enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R | KVM_PGTABLE_PROT_W;
> @@ -223,22 +242,7 @@ 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 +261,8 @@ 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;
> --
> 2.32.0.432.gabb21c7263-goog
>