Re: [PATCH 11/20] KVM: arm64: Add a range to pKVM ownership selftest

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] The pKVM ownership selftest crashes the hypervisor during boot when testing block-granular ranges.
--

--- Patch [11]: [PATCH 11/20] KVM: arm64: Add a range to pKVM ownership selftest ---
commit e6586b2867cba4559d50173770f2de71da4f2380
Author: Vincent Donnefort <[email protected]>

KVM: arm64: Add a range to pKVM ownership selftest

Extends pkvm_ownership_selftest() with a nr_pages argument to test state
transitions with both page-granular and block-granular ranges.

> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index a53600c853d4f..d5ee079a5d70d 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
[ ... ]
> @@ -1894,10 +1901,10 @@ int __pkvm_ownership_selftest(u64 pfn, u64 pgtable_pfn, unsigned long pgtable_nr
>  
>  	selftest_state.host = PKVM_PAGE_OWNED;
>  	selftest_state.guest[0] = PKVM_POISON;
>  	assert_transition_res(0,	__pkvm_host_force_reclaim_page_guest, phys);

[Severity: High]
Will this crash the hypervisor during boot when testing block-granular ranges?

When the selftest executes with a block-level range via PMD_ORDER, this
assertion expects __pkvm_host_force_reclaim_page_guest() to return 0. However,
__pkvm_host_force_reclaim_page_guest() hardcodes PAGE_SIZE internally:

arch/arm64/kvm/hyp/nvhe/mem_protect.c:__pkvm_host_force_reclaim_page_guest() {
    ...
    ret = get_valid_guest_pte(vm, ipa, PAGE_SIZE, &pte, &pa);
    ...
}

Because the mapping installed for this run is block-granular,
get_valid_guest_pte() will return -E2BIG. This causes assert_transition_res()
to fail, which triggers a WARN_ON at EL2. Since WARN_ON expands to a fatal
BRK instruction at EL2, this results in a hypervisor panic during boot.

[ ... ]
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> index a9645480d1648..4d41a16cd5962 100644
> --- a/arch/arm64/kvm/pkvm.c
> +++ b/arch/arm64/kvm/pkvm.c
[ ... ]
> @@ -274,17 +283,9 @@ void __init pkvm_ownership_selftest(void)
>  	/* Memory for the VM page-table */
>  	pgtable = __get_free_pages(GFP_KERNEL, pgtable_order);
>  	if (!pgtable)
> -		goto out;
> -
> -	/* Page whose ownership will be tested */
> -	page = __get_free_page(GFP_KERNEL);
> -	if (!page)
> -		goto out;
> +		return;
>  
> -	ret = kvm_call_hyp_nvhe(__pkvm_ownership_selftest, virt_to_pfn((void *)page),
> -				virt_to_pfn((void *)pgtable), 1 << pgtable_order);
> -out:
> -	if (ret)
> -		kvm_err("Failed to run %s (%ld)\n", __func__, ret);
> +	__pkvm_ownership_selftest(0, pgtable, pgtable_order);
> +	__pkvm_ownership_selftest(PMD_ORDER, pgtable, pgtable_order);
>  
>  	free_pages(pgtable, pgtable_order);
> -	free_page(page);
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=11