From 074c008007197297aaff9dd93627fb89b27d21e5 Mon Sep 17 00:00:00 2001 From: Ben Gardon Date: Wed, 2 Nov 2022 20:53:59 +0000 Subject: KVM: x86: Use SRCU to protect zap in __kvm_set_or_clear_apicv_inhibit() kvm_zap_gfn_range() must be called in an SRCU read-critical section, but there is no SRCU annotation in __kvm_set_or_clear_apicv_inhibit(). This can lead to the following warning via kvm_arch_vcpu_ioctl_set_guest_debug() if a Shadow MMU is in use (TDP MMU disabled or nesting): [ 1416.659809] ============================= [ 1416.659810] WARNING: suspicious RCU usage [ 1416.659839] 6.1.0-dbg-DEV #1 Tainted: G S I [ 1416.659853] ----------------------------- [ 1416.659854] include/linux/kvm_host.h:954 suspicious rcu_dereference_check() usage! [ 1416.659856] ... [ 1416.659904] dump_stack_lvl+0x84/0xaa [ 1416.659910] dump_stack+0x10/0x15 [ 1416.659913] lockdep_rcu_suspicious+0x11e/0x130 [ 1416.659919] kvm_zap_gfn_range+0x226/0x5e0 [ 1416.659926] ? kvm_make_all_cpus_request_except+0x18b/0x1e0 [ 1416.659935] __kvm_set_or_clear_apicv_inhibit+0xcc/0x100 [ 1416.659940] kvm_arch_vcpu_ioctl_set_guest_debug+0x350/0x390 [ 1416.659946] kvm_vcpu_ioctl+0x2fc/0x620 [ 1416.659955] __se_sys_ioctl+0x77/0xc0 [ 1416.659962] __x64_sys_ioctl+0x1d/0x20 [ 1416.659965] do_syscall_64+0x3d/0x80 [ 1416.659969] entry_SYSCALL_64_after_hwframe+0x63/0xcd Always take the KVM SRCU read lock in __kvm_set_or_clear_apicv_inhibit() to protect the GFN to memslot translation. The SRCU read lock is not technically required when no Shadow MMUs are in use, since the TDP MMU walks the paging structures from the roots and does not need to look up GFN translations in the memslots, but make the SRCU locking unconditional for simplicty. In most cases, the SRCU locking is taken care of in the vCPU run loop, but when called through other ioctls (such as KVM_SET_GUEST_DEBUG) there is no srcu_read_lock. Tested: ran tools/testing/selftests/kvm/x86_64/debug_regs on a DBG build. This patch causes the suspicious RCU warning to disappear. Note that the warning is hit in __kvm_zap_rmaps(), so kvm_memslots_have_rmaps() must return true in order for this to repro (i.e. the TDP MMU must be off or nesting in use.) Reported-by: Greg Thelen Fixes: 36222b117e36 ("KVM: x86: don't disable APICv memslot when inhibited") Signed-off-by: Ben Gardon Message-Id: <20221102205359.1260980-1-bgardon@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 521b433f978c..5f5eb577d583 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10404,7 +10404,10 @@ void __kvm_set_or_clear_apicv_inhibit(struct kvm *kvm, kvm->arch.apicv_inhibit_reasons = new; if (new) { unsigned long gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE); + int idx = srcu_read_lock(&kvm->srcu); + kvm_zap_gfn_range(kvm, gfn, gfn+1); + srcu_read_unlock(&kvm->srcu, idx); } } else { kvm->arch.apicv_inhibit_reasons = new; -- cgit v1.2.3