linux-kernel - Re: [PATCH v3 07/15] KVM: arm64: Introduce kvm_share

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Message-ID: <20211209111309.GB1912@willie-the-truck>
Date:   Thu, 9 Dec 2021 11:13:10 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 07/15] KVM: arm64: Introduce kvm_share_hyp()

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@...gle.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