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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id f7sm25241980wrg.34.2021.05.10.04.15.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 May 2021 04:15:14 -0700 (PDT) From: Vitaly Kuznetsov To: Wanpeng Li Cc: Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel , LKML , kvm Subject: Re: [PATCH] KVM: x86: hyper-v: Task srcu lock when accessing kvm_memslots() In-Reply-To: References: <1620634919-4563-1-git-send-email-wanpengli@tencent.com> <87mtt3vus5.fsf@vitty.brq.redhat.com> Date: Mon, 10 May 2021 13:15:13 +0200 Message-ID: <87k0o6x2ke.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wanpeng Li writes: > On Mon, 10 May 2021 at 16:48, Vitaly Kuznetsov wrote: >> >> Wanpeng Li writes: >> >> > From: Wanpeng Li >> > >> > 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 >> > --- >> > 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); >> >> Thanks! >> >> Do we need to do the same in kvm_hv_setup_tsc_page()? > > kvm_hv_setup_tsc_page() is called in vcpu_enter_guest() path which has > already held kvm->srcu lock. > I, true, thanks for checking! For the patch: Reviewed-by: Vitaly Kuznetsov -- Vitaly