From: Oliver Upton <oliver.upton@linux.dev> To: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>, Alexandru Elisei <alexandru.elisei@arm.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Oliver Upton <oliver.upton@linux.dev>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org> Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, Marek Szyprowski <m.szyprowski@samsung.com> Subject: [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Date: Tue, 15 Nov 2022 22:55:02 +0000 [thread overview] Message-ID: <20221115225502.2240227-1-oliver.upton@linux.dev> (raw) 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@samsung.com> Signed-off-by: Oliver Upton <oliver.upton@linux.dev> --- Applies on top of the parallel faults series that was picked up last week. Tested with kvm-arm.mode={nvhe,protected} on an Ampere Altra system. v1 -> v2: - Took Will's suggestion of conditioning RCU on a flag, small tweak to use existing bit instead (Thanks!) arch/arm64/include/asm/kvm_pgtable.h | 22 ++++++++++++++++------ arch/arm64/kvm/hyp/pgtable.c | 5 +++-- 2 files changed, 19 insertions(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h index a874ce0ce7b5..d4c7321fa652 100644 --- a/arch/arm64/include/asm/kvm_pgtable.h +++ b/arch/arm64/include/asm/kvm_pgtable.h @@ -51,8 +51,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared 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(bool shared) +{ + /* + * Due to the lack of RCU (or a similar protection scheme), only + * non-shared table walkers are allowed in the hypervisor. + */ + WARN_ON(shared); +} + +static inline void kvm_pgtable_walk_end(bool shared) {} static inline bool kvm_pgtable_walk_lock_held(void) { @@ -68,14 +76,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared return rcu_dereference_check(pteref, !shared); } -static inline void kvm_pgtable_walk_begin(void) +static inline void kvm_pgtable_walk_begin(bool shared) { - rcu_read_lock(); + if (shared) + rcu_read_lock(); } -static inline void kvm_pgtable_walk_end(void) +static inline void kvm_pgtable_walk_end(bool shared) { - rcu_read_unlock(); + if (shared) + rcu_read_unlock(); } static inline bool kvm_pgtable_walk_lock_held(void) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 5bca9610d040..16aed10e7e59 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -287,11 +287,12 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size, .end = PAGE_ALIGN(walk_data.addr + size), .walker = walker, }; + bool shared = walker->flags & KVM_PGTABLE_WALK_SHARED; int r; - kvm_pgtable_walk_begin(); + kvm_pgtable_walk_begin(shared); r = _kvm_pgtable_walk(pgt, &walk_data); - kvm_pgtable_walk_end(); + kvm_pgtable_walk_end(shared); return r; } -- 2.38.1.431.g37b22c650d-goog _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: Oliver Upton <oliver.upton@linux.dev> To: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>, Alexandru Elisei <alexandru.elisei@arm.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Oliver Upton <oliver.upton@linux.dev>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org> Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, kvmarm@lists.linux.dev, Marek Szyprowski <m.szyprowski@samsung.com>, linux-kernel@vger.kernel.org Subject: [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Date: Tue, 15 Nov 2022 22:55:02 +0000 [thread overview] Message-ID: <20221115225502.2240227-1-oliver.upton@linux.dev> (raw) Message-ID: <20221115225502.IOWyQaRq3QJ172gi2NAZjXK3KJC70oaQ8LzhXYABDSw@z> (raw) 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@samsung.com> Signed-off-by: Oliver Upton <oliver.upton@linux.dev> --- Applies on top of the parallel faults series that was picked up last week. Tested with kvm-arm.mode={nvhe,protected} on an Ampere Altra system. v1 -> v2: - Took Will's suggestion of conditioning RCU on a flag, small tweak to use existing bit instead (Thanks!) arch/arm64/include/asm/kvm_pgtable.h | 22 ++++++++++++++++------ arch/arm64/kvm/hyp/pgtable.c | 5 +++-- 2 files changed, 19 insertions(+), 8 deletions(-) diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h index a874ce0ce7b5..d4c7321fa652 100644 --- a/arch/arm64/include/asm/kvm_pgtable.h +++ b/arch/arm64/include/asm/kvm_pgtable.h @@ -51,8 +51,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared 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(bool shared) +{ + /* + * Due to the lack of RCU (or a similar protection scheme), only + * non-shared table walkers are allowed in the hypervisor. + */ + WARN_ON(shared); +} + +static inline void kvm_pgtable_walk_end(bool shared) {} static inline bool kvm_pgtable_walk_lock_held(void) { @@ -68,14 +76,16 @@ static inline kvm_pte_t *kvm_dereference_pteref(kvm_pteref_t pteref, bool shared return rcu_dereference_check(pteref, !shared); } -static inline void kvm_pgtable_walk_begin(void) +static inline void kvm_pgtable_walk_begin(bool shared) { - rcu_read_lock(); + if (shared) + rcu_read_lock(); } -static inline void kvm_pgtable_walk_end(void) +static inline void kvm_pgtable_walk_end(bool shared) { - rcu_read_unlock(); + if (shared) + rcu_read_unlock(); } static inline bool kvm_pgtable_walk_lock_held(void) diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 5bca9610d040..16aed10e7e59 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -287,11 +287,12 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size, .end = PAGE_ALIGN(walk_data.addr + size), .walker = walker, }; + bool shared = walker->flags & KVM_PGTABLE_WALK_SHARED; int r; - kvm_pgtable_walk_begin(); + kvm_pgtable_walk_begin(shared); r = _kvm_pgtable_walk(pgt, &walk_data); - kvm_pgtable_walk_end(); + kvm_pgtable_walk_end(shared); return r; } -- 2.38.1.431.g37b22c650d-goog
next reply other threads:[~2022-11-15 22:55 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-11-15 22:55 Oliver Upton [this message] 2022-11-15 22:55 ` [PATCH v2] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Oliver Upton 2022-11-16 3:08 ` Marc Zyngier 2022-11-16 3:08 ` Marc Zyngier 2022-11-16 7:27 ` Oliver Upton 2022-11-16 7:27 ` Oliver Upton 2022-11-16 8:14 ` Oliver Upton 2022-11-16 8:14 ` Oliver Upton
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