Re: [PATCH 14/30] KVM: arm64: Hook up reclaim hypercall to pkvm_pgtable_stage2_destroy()

Will Deacon
2026-01-09T14:36:03Z

On Tue, Jan 06, 2026 at 02:59:19PM +0000, Quentin Perret wrote:
> On Monday 05 Jan 2026 at 15:49:22 (+0000), Will Deacon wrote:
> > During teardown of a protected guest, its memory pages must be reclaimed
> > from the hypervisor by issuing the '__pkvm_reclaim_dying_guest_page'
> > hypercall.
> >
> > Add a new helper, __pkvm_pgtable_stage2_reclaim(), which is called
> > during the VM teardown operation to reclaim pages from the hypervisor
> > and drop the GUP pin on the host.
> >
> > Signed-off-by: Will Deacon <will@kernel.org>
> > ---
> > arch/arm64/kvm/pkvm.c | 31 ++++++++++++++++++++++++++++++-
> > 1 file changed, 30 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
> > index 1814e17d600e..8be91051699e 100644
> > --- a/arch/arm64/kvm/pkvm.c
> > +++ b/arch/arm64/kvm/pkvm.c
> > @@ -322,6 +322,32 @@ int pkvm_pgtable_stage2_init(struct kvm_pgtable *pgt, struct kvm_s2_mmu *mmu,
> > return 0;
> > }
> >
> > +static int __pkvm_pgtable_stage2_reclaim(struct kvm_pgtable *pgt, u64 start, u64 end)
> > +{
> > + struct kvm *kvm = kvm_s2_mmu_to_kvm(pgt->mmu);
> > + pkvm_handle_t handle = kvm->arch.pkvm.handle;
> > + struct pkvm_mapping *mapping;
> > + int ret;
> > +
> > + for_each_mapping_in_range_safe(pgt, start, end, mapping) {
> > + struct page *page;
> > +
> > + ret = kvm_call_hyp_nvhe(__pkvm_reclaim_dying_guest_page,
> > + handle, mapping->gfn);
> > + if (WARN_ON(ret))
> > + return ret;
> > +
> > + page = pfn_to_page(mapping->pfn);
> > + WARN_ON_ONCE(mapping->nr_pages != 1);
> > + unpin_user_pages_dirty_lock(&page, 1, true);
> > + account_locked_vm(current->mm, 1, false);
> > + pkvm_mapping_remove(mapping, &pgt->pkvm_mappings);
> > + kfree(mapping);
>
> Nit: this might take a while, worth adding a cond_resched() in here?

Commit 4ddfab5436b6 ("KVM: arm64: Reschedule as needed when destroying
the stage-2 page-tables") breaks the destruction operation up into
chunks so we now reschedule from the caller in stage2_destroy_range().

Do you think we need an additional reschedule?

Will