linux-kernel - Re: [PATCH v2 3/9] KVM: arm64: Add a range to __pkvm_host_unshare

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Message-ID: <Z-6p49EcsZKid7L1@google.com>
Date: Thu, 3 Apr 2025 15:31:47 +0000
From: Quentin Perret <qperret@...gle.com>
To: Vincent Donnefort <vdonnefort@...gle.com>
Cc: maz@...nel.org, oliver.upton@...ux.dev, joey.gouly@....com,
	suzuki.poulose@....com, yuzenghui@...wei.com,
	catalin.marinas@....com, will@...nel.org,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v2 3/9] KVM: arm64: Add a range to
 __pkvm_host_unshare_guest()

On Thursday 06 Mar 2025 at 11:00:32 (+0000), Vincent Donnefort wrote:
> @@ -1012,51 +1011,52 @@ static int __check_host_shared_guest(struct pkvm_hyp_vm *vm, u64 *__phys, u64 ip
>  		return ret;
>  	if (!kvm_pte_valid(pte))
>  		return -ENOENT;
> -	if (level != KVM_PGTABLE_LAST_LEVEL)
> +	if (kvm_granule_size(level) != size)
>  		return -E2BIG;
>  
> -	state = guest_get_page_state(pte, ipa);
> -	if (state != PKVM_PAGE_SHARED_BORROWED)
> -		return -EPERM;
> +	ret = __guest_check_page_state_range(vm, ipa, size, PKVM_PAGE_SHARED_BORROWED);
> +	if (ret)
> +		return ret;

Given that hard rely on kvm_granule_size(level) == size above, we should
be guaranteed that the PTE covers the entire range we're interested in.
So is there a point in starting a new page-table walk here? Could we
just keep guest_get_page_state() directly?

>  
>  	phys = kvm_pte_to_phys(pte);
> -	ret = check_range_allowed_memory(phys, phys + PAGE_SIZE);
> +	ret = check_range_allowed_memory(phys, phys + size);
>  	if (WARN_ON(ret))
>  		return ret;
>  
> -	page = hyp_phys_to_page(phys);
> -	if (page->host_state != PKVM_PAGE_SHARED_OWNED)
> -		return -EPERM;
> -	if (WARN_ON(!page->host_share_guest_count))
> -		return -EINVAL;
> +	for_each_hyp_page(phys, size, page) {
> +		if (page->host_state != PKVM_PAGE_SHARED_OWNED)
> +			return -EPERM;
> +		if (WARN_ON(!page->host_share_guest_count))
> +			return -EINVAL;
> +	}
>  
>  	*__phys = phys;
>  
>  	return 0;
>  }