[PATCH 5.12 287/296] KVM: X86: hyper-v: Task srcu lock when accessing kvm_memslots()

Greg Kroah-Hartman
2021-05-31T16:51:16Z

From: Wanpeng Li <wanpengli@tencent.com>

[ Upstream commit da6d63a0062a3ee721b84123b83ec093f25759b0 ]

WARNING: suspicious RCU usage
5.13.0-rc1 #4 Not tainted
-----------------------------
./include/linux/kvm_host.h:710 suspicious rcu_dereference_check() usage!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by hyperv_clock/8318:
#0: ffffb6b8cb05a7d8 (&hv->hv_lock){+.+.}-{3:3}, at: kvm_hv_invalidate_tsc_page+0x3e/0xa0 [kvm]

stack backtrace:
CPU: 3 PID: 8318 Comm: hyperv_clock Not tainted 5.13.0-rc1 #4
Call Trace:
dump_stack+0x87/0xb7
lockdep_rcu_suspicious+0xce/0xf0
kvm_write_guest_page+0x1c1/0x1d0 [kvm]
kvm_write_guest+0x50/0x90 [kvm]
kvm_hv_invalidate_tsc_page+0x79/0xa0 [kvm]
kvm_gen_update_masterclock+0x1d/0x110 [kvm]
kvm_arch_vm_ioctl+0x2a7/0xc50 [kvm]
kvm_vm_ioctl+0x123/0x11d0 [kvm]
__x64_sys_ioctl+0x3ed/0x9d0
do_syscall_64+0x3d/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae

kvm_memslots() will be called by kvm_write_guest(), so we should take the srcu lock.

Fixes: e880c6ea5 (KVM: x86: hyper-v: Prevent using not-yet-updated TSC page by secondary CPUs)
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1621339235-11131-4-git-send-email-wanpengli@tencent.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/kvm/hyperv.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index f98370a39936..f00830e5202f 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1172,6 +1172,7 @@ void kvm_hv_invalidate_tsc_page(struct kvm *kvm)
{
struct kvm_hv *hv = to_kvm_hv(kvm);
u64 gfn;
+ int idx;

if (hv->hv_tsc_page_status == HV_TSC_PAGE_BROKEN ||
hv->hv_tsc_page_status == HV_TSC_PAGE_UNSET ||
@@ -1190,9 +1191,16 @@ void kvm_hv_invalidate_tsc_page(struct kvm *kvm)
gfn = hv->hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;

hv->tsc_ref.tsc_sequence = 0;
+
+ /*
+ * Take the srcu lock as memslots will be accessed to check the gfn
+ * cache generation against the memslots generation.
+ */
+ idx = srcu_read_lock(&kvm->srcu);
if (kvm_write_guest(kvm, gfn_to_gpa(gfn),
&hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence)))
hv->hv_tsc_page_status = HV_TSC_PAGE_BROKEN;
+ srcu_read_unlock(&kvm->srcu, idx);

out_unlock:
mutex_unlock(&hv->hv_lock);
--
2.30.2