3.16.51-rc1 review patch. If anyone has any objections, please let me know.
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From: Boqun Feng boqun.feng@gmail.com
commit a2b7861bb33b2538420bb5d8554153484d3f961f upstream.
Currently, in PREEMPT_COUNT=n kernel, kvm_async_pf_task_wait() could call schedule() to reschedule in some cases. This could result in accidentally ending the current RCU read-side critical section early, causing random memory corruption in the guest, or otherwise preempting the currently running task inside between preempt_disable and preempt_enable.
The difficulty to handle this well is because we don't know whether an async PF delivered in a preemptible section or RCU read-side critical section for PREEMPT_COUNT=n, since preempt_disable()/enable() and rcu_read_lock/unlock() are both no-ops in that case.
To cure this, we treat any async PF interrupting a kernel context as one that cannot be preempted, preventing kvm_async_pf_task_wait() from choosing the schedule() path in that case.
To do so, a second parameter for kvm_async_pf_task_wait() is introduced, so that we know whether it's called from a context interrupting the kernel, and the parameter is set properly in all the callsites.
Cc: "Paul E. McKenney" paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Boqun Feng boqun.feng@gmail.com Signed-off-by: Radim Krčmář rkrcmar@redhat.com [bwh: Backported to 3.16: - Use user_mode_vm() as equivalent to upstream user_mode() - Adjust filename, context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/x86/include/asm/kvm_para.h | 4 ++-- arch/x86/kernel/kvm.c | 14 ++++++++++---- arch/x86/kvm/svm.c | 2 +- 3 files changed, 13 insertions(+), 7 deletions(-)
--- a/arch/x86/include/asm/kvm_para.h +++ b/arch/x86/include/asm/kvm_para.h @@ -95,7 +95,7 @@ static inline long kvm_hypercall4(unsign bool kvm_para_available(void); unsigned int kvm_arch_para_features(void); void __init kvm_guest_init(void); -void kvm_async_pf_task_wait(u32 token); +void kvm_async_pf_task_wait(u32 token, int interrupt_kernel); void kvm_async_pf_task_wake(u32 token); u32 kvm_read_and_reset_pf_reason(void); extern void kvm_disable_steal_time(void); @@ -110,7 +110,7 @@ static inline void kvm_spinlock_init(voi
#else /* CONFIG_KVM_GUEST */ #define kvm_guest_init() do {} while (0) -#define kvm_async_pf_task_wait(T) do {} while(0) +#define kvm_async_pf_task_wait(T, I) do {} while(0) #define kvm_async_pf_task_wake(T) do {} while(0)
static inline bool kvm_para_available(void) --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -116,7 +116,11 @@ static struct kvm_task_sleep_node *_find return NULL; }
-void kvm_async_pf_task_wait(u32 token) +/* + * @interrupt_kernel: Is this called from a routine which interrupts the kernel + * (other than user space)? + */ +void kvm_async_pf_task_wait(u32 token, int interrupt_kernel) { u32 key = hash_32(token, KVM_TASK_SLEEP_HASHBITS); struct kvm_task_sleep_head *b = &async_pf_sleepers[key]; @@ -139,8 +143,10 @@ void kvm_async_pf_task_wait(u32 token)
n.token = token; n.cpu = smp_processor_id(); - n.halted = is_idle_task(current) || preempt_count() > 1 || - rcu_preempt_depth(); + n.halted = is_idle_task(current) || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) + ? preempt_count() > 1 || rcu_preempt_depth() + : interrupt_kernel); init_waitqueue_head(&n.wq); hlist_add_head(&n.link, &b->list); spin_unlock(&b->lock); @@ -269,7 +275,7 @@ do_async_page_fault(struct pt_regs *regs /* page is swapped out by the host. */ prev_state = exception_enter(); exit_idle(); - kvm_async_pf_task_wait((u32)read_cr2()); + kvm_async_pf_task_wait((u32)read_cr2(), !user_mode_vm(regs)); exception_exit(prev_state); break; case KVM_PV_REASON_PAGE_READY: --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -1718,7 +1718,7 @@ static int pf_interception(struct vcpu_s case KVM_PV_REASON_PAGE_NOT_PRESENT: svm->apf_reason = 0; local_irq_disable(); - kvm_async_pf_task_wait(fault_address); + kvm_async_pf_task_wait(fault_address, 0); local_irq_enable(); break; case KVM_PV_REASON_PAGE_READY: