Re: [PATCH v2 25/35] KVM: arm64: Reclaim faulting page from pKVM in spurious fault handler

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Will,

Would be nice to merge this with the previous patch, that added the force
reclaim function, as it would make reviewing easier.

On Mon, Jan 19, 2026 at 12:46:18PM +0000, Will Deacon wrote:
> Host kernel accesses to pages that are inaccessible at stage-2 result in
> the injection of a translation fault, which is fatal unless an exception
> table fixup is registered for the faulting PC (e.g. for user access
> routines). This is undesirable, since a get_user_pages() call could be
> used to obtain a reference to a donated page and then a subsequent
> access via a kernel mapping would lead to a panic().
> 
> Rework the spurious fault handler so that stage-2 faults injected back
> into the host result in the target page being forcefully reclaimed when
> no exception table fixup handler is registered.
> 
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>  arch/arm64/include/asm/virt.h |  6 ++++++
>  arch/arm64/kvm/pkvm.c         |  7 +++++++
>  arch/arm64/mm/fault.c         | 15 +++++++++------
>  3 files changed, 22 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index b51ab6840f9c..e80addc923a4 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -94,6 +94,12 @@ static inline bool is_pkvm_initialized(void)
>  	       static_branch_likely(&kvm_protected_mode_initialized);
>  }
>  
> +#ifdef CONFIG_KVM
> +bool pkvm_reclaim_guest_page(phys_addr_t phys);
> +#else
> +static inline bool pkvm_reclaim_guest_page(phys_addr_t phys) { return false; }
> +#endif
> +
>  /* Reports the availability of HYP mode */
>  static inline bool is_hyp_mode_available(void)
>  {
> diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> index 8be91051699e..d1926cb08c76 100644
> --- a/arch/arm64/kvm/pkvm.c
> +++ b/arch/arm64/kvm/pkvm.c
> @@ -563,3 +563,10 @@ int pkvm_pgtable_stage2_split(struct kvm_pgtable *pgt, u64 addr, u64 size,
>  	WARN_ON_ONCE(1);
>  	return -EINVAL;
>  }
> +
> +bool pkvm_reclaim_guest_page(phys_addr_t phys)
> +{
> +	int ret = kvm_call_hyp_nvhe(__pkvm_force_reclaim_guest_page, phys);

Nitpicking here, we have the functions __pkvm_reclaim_page_guest() and this
function, pkvm_reclaim_guest_page(), which calls
__pkvm_force_reclaim_guest_page, which in turn calls
__pkvm_host_force_reclaim_page_guest(). I think having a bit of naming
consistency would be really useful when navigating the source code.

It might also be useful to document that callers of the hypercall
__pkvm_force_reclaim_guest_page are not expected to unpin the page in case of
success, but callers of __pkvm_reclaim_dying_guest_page are.

Thanks,
Alex

> +
> +	return !ret || ret == -EAGAIN;
> +}
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 2294f2061866..5d62abee5262 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -289,9 +289,6 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
>  	if (!is_el1_data_abort(esr) || !esr_fsc_is_translation_fault(esr))
>  		return false;
>  
> -	if (is_pkvm_stage2_abort(esr))
> -		return false;
> -
>  	local_irq_save(flags);
>  	asm volatile("at s1e1r, %0" :: "r" (addr));
>  	isb();
> @@ -302,8 +299,12 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
>  	 * If we now have a valid translation, treat the translation fault as
>  	 * spurious.
>  	 */
> -	if (!(par & SYS_PAR_EL1_F))
> +	if (!(par & SYS_PAR_EL1_F)) {
> +		if (is_pkvm_stage2_abort(esr))
> +			return pkvm_reclaim_guest_page(par & SYS_PAR_EL1_PA);
> +
>  		return true;
> +	}
>  
>  	/*
>  	 * If we got a different type of fault from the AT instruction,
> @@ -389,9 +390,11 @@ static void __do_kernel_fault(unsigned long addr, unsigned long esr,
>  	if (!is_el1_instruction_abort(esr) && fixup_exception(regs, esr))
>  		return;
>  
> -	if (WARN_RATELIMIT(is_spurious_el1_translation_fault(addr, esr, regs),
> -	    "Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
> +	if (is_spurious_el1_translation_fault(addr, esr, regs)) {
> +		WARN_RATELIMIT(!is_pkvm_stage2_abort(esr),
> +			"Ignoring spurious kernel translation fault at virtual address %016lx\n", addr);
>  		return;
> +	}
>  
>  	if (is_el1_mte_sync_tag_check_fault(esr)) {
>  		do_tag_recovery(addr, esr, regs);
> -- 
> 2.52.0.457.g6b5491de43-goog
> 
>