linux-kernel - Re: [PATCH 12/14] KVM: arm64: Refactor pkvm

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Date:   Wed, 21 Jul 2021 09:37:58 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        dbrazdil@...gle.com, kernel-team@...roid.com
Subject: Re: [PATCH 12/14] KVM: arm64: Refactor pkvm_pgtable locking

Hi Quentin,

On Mon, Jul 19, 2021 at 11:48 AM Quentin Perret <qperret@...gle.com> wrote:
>
> Refactor the hypervisor stage-1 locking in nVHE protected mode to expose
> a new pkvm_create_mappings_locked() function. This will be used in later
> patches to allow walking and changing the hypervisor stage-1 without
> releasing the lock.
>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/kvm/hyp/include/nvhe/mm.h |  1 +
>  arch/arm64/kvm/hyp/nvhe/mm.c         | 16 ++++++++++++++--
>  2 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> index 8ec3a5a7744b..c76d7136ed9b 100644
> --- a/arch/arm64/kvm/hyp/include/nvhe/mm.h
> +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h
> @@ -23,6 +23,7 @@ int hyp_map_vectors(void);
>  int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back);
>  int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot);
>  int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot);
> +int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot);
>  int __pkvm_create_mappings(unsigned long start, unsigned long size,
>                            unsigned long phys, enum kvm_pgtable_prot prot);
>  unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,

The locking logic seems to be consistent, with pkvm_create_mappings()
holding the lock for the whole duration of the operation rather than
per-iteration.

It would be nice though to document which lock should be held for the
_locked versions.

Thanks,
/fuad




> diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
> index a8efdf0f9003..dde22e2a322a 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mm.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mm.c
> @@ -67,7 +67,7 @@ unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size,
>         return addr;
>  }
>
> -int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
> +int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot)
>  {
>         unsigned long start = (unsigned long)from;
>         unsigned long end = (unsigned long)to;
> @@ -81,7 +81,8 @@ int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
>                 int err;
>
>                 phys = hyp_virt_to_phys((void *)virt_addr);
> -               err = __pkvm_create_mappings(virt_addr, PAGE_SIZE, phys, prot);
> +               err = kvm_pgtable_hyp_map(&pkvm_pgtable, virt_addr, PAGE_SIZE,
> +                                         phys, prot);
>                 if (err)
>                         return err;
>         }
> @@ -89,6 +90,17 @@ int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
>         return 0;
>  }
>
> +int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot)
> +{
> +       int ret;
> +
> +       hyp_spin_lock(&pkvm_pgd_lock);
> +       ret = pkvm_create_mappings_locked(from, to, prot);
> +       hyp_spin_unlock(&pkvm_pgd_lock);
> +
> +       return ret;
> +}
> +
>  int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back)
>  {
>         unsigned long start, end;
> --
> 2.32.0.402.g57bb445576-goog
>