Re: [PATCH v3 07/15] KVM: arm64: Introduce kvm_share_hyp()

Will Deacon
2021-12-09T11:14:37Z

On Wed, Dec 01, 2021 at 05:04:01PM +0000, Quentin Perret wrote:
> The create_hyp_mappings() function can currently be called at any point
> in time. However, its behaviour in protected mode changes widely
> depending on when it is being called. Prior to KVM init, it is used to
> create the temporary page-table used to bring-up the hypervisor, and
> later on it is transparently turned into a 'share' hypercall when the
> kernel has lost control over the hypervisor stage-1. In order to prepare
> the ground for also unsharing pages with the hypervisor during guest
> teardown, introduce a kvm_share_hyp() function to make it clear in which
> places a share hypercall should be expected, as we will soon need a
> matching unshare hypercall in all those places.
>
> Signed-off-by: Quentin Perret <qperret@google.com>
> ---
> arch/arm64/include/asm/kvm_mmu.h | 1 +
> arch/arm64/kvm/arm.c | 4 ++--
> arch/arm64/kvm/fpsimd.c | 2 +-
> arch/arm64/kvm/mmu.c | 27 +++++++++++++++++++++------
> arch/arm64/kvm/reset.c | 2 +-
> 5 files changed, 26 insertions(+), 10 deletions(-)

[...]

> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index f8f1096a297f..fd868fb9d922 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -299,6 +299,25 @@ static int pkvm_share_hyp(phys_addr_t start, phys_addr_t end)
> return 0;
> }
>
> +int kvm_share_hyp(void *from, void *to)
> +{
> + if (is_kernel_in_hyp_mode())
> + return 0;
> +
> + /*
> + * The share hcall maps things in the 'fixed-offset' region of the hyp
> + * VA space, so we can only share physically contiguous data-structures
> + * for now.
> + */
> + if (is_vmalloc_addr(from) || is_vmalloc_addr(to))
> + return -EINVAL;

If we're adding these sanity checks, perhaps is_vmalloc_or_module_addr()
would be worth using instead?

Will