On Wed, Nov 16, 2022 at 04:56:55PM +0000, Oliver Upton wrote: > Marek reported a BUG resulting from the recent parallel faults changes, > as the hyp stage-1 map walker attempted to allocate table memory while > holding the RCU read lock: > > BUG: sleeping function called from invalid context at > include/linux/sched/mm.h:274 > in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0 > preempt_count: 0, expected: 0 > RCU nest depth: 1, expected: 0 > 2 locks held by swapper/0/1: > #0: ffff80000a8a44d0 (kvm_hyp_pgd_mutex){+.+.}-{3:3}, at: > __create_hyp_mappings+0x80/0xc4 > #1: ffff80000a927720 (rcu_read_lock){....}-{1:2}, at: > kvm_pgtable_walk+0x0/0x1f4 > CPU: 2 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc3+ #5918 > Hardware name: Raspberry Pi 3 Model B (DT) > Call trace: > dump_backtrace.part.0+0xe4/0xf0 > show_stack+0x18/0x40 > dump_stack_lvl+0x8c/0xb8 > dump_stack+0x18/0x34 > __might_resched+0x178/0x220 > __might_sleep+0x48/0xa0 > prepare_alloc_pages+0x178/0x1a0 > __alloc_pages+0x9c/0x109c > alloc_page_interleave+0x1c/0xc4 > alloc_pages+0xec/0x160 > get_zeroed_page+0x1c/0x44 > kvm_hyp_zalloc_page+0x14/0x20 > hyp_map_walker+0xd4/0x134 > kvm_pgtable_visitor_cb.isra.0+0x38/0x5c > __kvm_pgtable_walk+0x1a4/0x220 > kvm_pgtable_walk+0x104/0x1f4 > kvm_pgtable_hyp_map+0x80/0xc4 > __create_hyp_mappings+0x9c/0xc4 > kvm_mmu_init+0x144/0x1cc > kvm_arch_init+0xe4/0xef4 > kvm_init+0x3c/0x3d0 > arm_init+0x20/0x30 > do_one_initcall+0x74/0x400 > kernel_init_freeable+0x2e0/0x350 > kernel_init+0x24/0x130 > ret_from_fork+0x10/0x20 > > Since the hyp stage-1 table walkers are serialized by kvm_hyp_pgd_mutex, > RCU protection really doesn't add anything. Don't acquire the RCU read > lock for an exclusive walk. While at it, add a warning which codifies > the lack of support for shared walks in the hypervisor code. > > Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> > Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx> > --- > arch/arm64/include/asm/kvm_pgtable.h | 22 ++++++++++++++++------ > arch/arm64/kvm/hyp/pgtable.c | 4 ++-- > 2 files changed, 18 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h > index f23af693e3c5..a07fc5e35a8c 100644 > --- a/arch/arm64/include/asm/kvm_pgtable.h > +++ b/arch/arm64/include/asm/kvm_pgtable.h > @@ -229,8 +229,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(struct kvm_pgtable_walker *walke > return pteref; > } > > -static inline void kvm_pgtable_walk_begin(void) {} > -static inline void kvm_pgtable_walk_end(void) {} > +static inline void kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker) > +{ > + /* > + * Due to the lack of RCU (or a similar protection scheme), only > + * non-shared table walkers are allowed in the hypervisor. > + */ > + WARN_ON(walker->flags & KVM_PGTABLE_WALK_SHARED); > +} I think it would be better to propagate the error to the caller rather than WARN here. Since you're rejigging things anyway, can you have this function return int? Will