linux-kernel - Re: [PATCH v3 19/21] KVM: arm64: Refactor protected nVHE stage-1 locking

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Date:   Tue, 3 Aug 2021 07:31:03 +0200
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 v3 19/21] KVM: arm64: Refactor protected nVHE stage-1 locking

Hi Quentin,

On Thu, Jul 29, 2021 at 3:29 PM 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         | 18 ++++++++++++++++--
>  2 files changed, 17 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,
> diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c
> index a8efdf0f9003..6fbe8e8030f6 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mm.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mm.c
> @@ -67,13 +67,15 @@ 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;
>         unsigned long virt_addr;
>         phys_addr_t phys;
>
> +       hyp_assert_lock_held(&pkvm_pgd_lock);
> +
>         start = start & PAGE_MASK;
>         end = PAGE_ALIGN(end);
>
> @@ -81,7 +83,8 @@ 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 +92,17 @@ 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;
> +}
> +

I'm wondering whether this patch should also refactor
__pkvm_create_mappings. It doesn't quite do the exact same thing and
has different parameters.

Thanks,
/fuad

>  int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back)
>  {
>         unsigned long start, end;
> --
> 2.32.0.432.gabb21c7263-goog
>