On Mon, Apr 18, 2022 at 7:55 PM Ricardo Koller <ricarkol@xxxxxxxxxx> wrote:
>
> On Fri, Apr 15, 2022 at 09:58:48PM +0000, Oliver Upton wrote:
> > Use RCU to safely traverse the page tables in parallel; the tables
> > themselves will only be freed from an RCU synchronized context. Don't
> > even bother with adding support to hyp, and instead just assume
> > exclusive access of the page tables.
> >
> > Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
> > ---
> > arch/arm64/kvm/hyp/pgtable.c | 23 ++++++++++++++++++++++-
> > 1 file changed, 22 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> > index 5b64fbca8a93..d4699f698d6e 100644
> > --- a/arch/arm64/kvm/hyp/pgtable.c
> > +++ b/arch/arm64/kvm/hyp/pgtable.c
> > @@ -132,9 +132,28 @@ static kvm_pte_t kvm_phys_to_pte(u64 pa)
> > return pte;
> > }
> >
> > +
> > +#if defined(__KVM_NVHE_HYPERVISOR__)
> > +static inline void kvm_pgtable_walk_begin(void)
> > +{}
> > +
> > +static inline void kvm_pgtable_walk_end(void)
> > +{}
> > +
> > +#define kvm_dereference_ptep rcu_dereference_raw
> > +#else
> > +#define kvm_pgtable_walk_begin rcu_read_lock
> > +
> > +#define kvm_pgtable_walk_end rcu_read_unlock
> > +
> > +#define kvm_dereference_ptep rcu_dereference
> > +#endif
> > +
> > static kvm_pte_t *kvm_pte_follow(kvm_pte_t pte, struct kvm_pgtable_mm_ops *mm_ops)
> > {
> > - return mm_ops->phys_to_virt(kvm_pte_to_phys(pte));
> > + kvm_pte_t __rcu *ptep = mm_ops->phys_to_virt(kvm_pte_to_phys(pte));
> > +
> > + return kvm_dereference_ptep(ptep);
> > }
> >
> > static void kvm_clear_pte(kvm_pte_t *ptep)
> > @@ -288,7 +307,9 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
> > .walker = walker,
> > };
> >
> > + kvm_pgtable_walk_begin();
> > return _kvm_pgtable_walk(&walk_data);
> > + kvm_pgtable_walk_end();
>
> This might be fixed later in the series, but at this point the
> rcu_read_unlock is never called.
Well that's embarrassing!
