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From:   Wanpeng Li <kernellwp@gmail.com>
To:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>
Subject: [PATCH] KVM: x86: hyper-v: Task srcu lock when accessing kvm_memslots()
Date:   Mon, 10 May 2021 16:21:59 +0800
Message-Id: <1620634919-4563-1-git-send-email-wanpengli@tencent.com>
Precedence: bulk

From: Wanpeng Li <wanpengli@tencent.com>

 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)
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
 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 f98370a3..f00830e 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);
-- 
2.7.4