Messages in this thread Patch in this message | | | Date | Fri, 31 Oct 2014 13:30:35 +0800 | From | "Chen, Tiejun" <> | Subject | Re: [PATCH] KVM: x86: fix access memslots w/o hold srcu read lock |
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On 2014/10/31 12:33, Wanpeng Li wrote: > The srcu read lock must be held while accessing memslots (e.g. > when using gfn_to_* functions), however, commit c24ae0dcd3e8 > ("kvm: x86: Unpin and remove kvm_arch->apic_access_page") call > gfn_to_page() in kvm_vcpu_reload_apic_access_page() w/o hold it > which leads to suspicious rcu_dereference_check() usage warning. > This patch fix it by holding srcu read lock when call gfn_to_page() > in kvm_vcpu_reload_apic_access_page() function. > > > [ INFO: suspicious RCU usage. ] > 3.18.0-rc2-test2+ #70 Not tainted > ------------------------------- > include/linux/kvm_host.h:474 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > rcu_scheduler_active = 1, debug_locks = 0 > 1 lock held by qemu-system-x86/2371: > #0: (&vcpu->mutex){+.+...}, at: [<ffffffffa037d800>] vcpu_load+0x20/0xd0 [kvm] > > stack backtrace: > CPU: 4 PID: 2371 Comm: qemu-system-x86 Not tainted 3.18.0-rc2-test2+ #70 > Hardware name: Dell Inc. OptiPlex 9010/0M9KCM, BIOS A12 01/10/2013 > 0000000000000001 ffff880209983ca8 ffffffff816f514f 0000000000000000 > ffff8802099b8990 ffff880209983cd8 ffffffff810bd687 00000000000fee00 > ffff880208a2c000 ffff880208a10000 ffff88020ef50040 ffff880209983d08 > Call Trace: > [<ffffffff816f514f>] dump_stack+0x4e/0x71 > [<ffffffff810bd687>] lockdep_rcu_suspicious+0xe7/0x120 > [<ffffffffa037d055>] gfn_to_memslot+0xd5/0xe0 [kvm] > [<ffffffffa03807d3>] __gfn_to_pfn+0x33/0x60 [kvm] > [<ffffffffa0380885>] gfn_to_page+0x25/0x90 [kvm] > [<ffffffffa038aeec>] kvm_vcpu_reload_apic_access_page+0x3c/0x80 [kvm] > [<ffffffffa08f0a9c>] vmx_vcpu_reset+0x20c/0x460 [kvm_intel] > [<ffffffffa039ab8e>] kvm_vcpu_reset+0x15e/0x1b0 [kvm] > [<ffffffffa039ac0c>] kvm_arch_vcpu_setup+0x2c/0x50 [kvm] > [<ffffffffa037f7e0>] kvm_vm_ioctl+0x1d0/0x780 [kvm] > [<ffffffff810bc664>] ? __lock_is_held+0x54/0x80 > [<ffffffff812231f0>] do_vfs_ioctl+0x300/0x520 > [<ffffffff8122ee45>] ? __fget+0x5/0x250 > [<ffffffff8122f0fa>] ? __fget_light+0x2a/0xe0 > [<ffffffff81223491>] SyS_ioctl+0x81/0xa0 > [<ffffffff816fed6d>] system_call_fastpath+0x16/0x1b > > Reported-by: Takashi Iwai <tiwai@suse.de> > Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> > Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com> > --- > arch/x86/kvm/x86.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0033df3..2d97329 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -6059,6 +6059,7 @@ static void kvm_vcpu_flush_tlb(struct kvm_vcpu *vcpu) > void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu) > { > struct page *page = NULL; > + int idx; > > if (!irqchip_in_kernel(vcpu->kvm)) > return; > @@ -6066,7 +6067,9 @@ void kvm_vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu) > if (!kvm_x86_ops->set_apic_access_page_addr) > return; > > + idx = srcu_read_lock(&vcpu->kvm->srcu);
There's another scenario that we already hold srcu before call kvm_vcpu_reload_apic_access_page(),
__vcpu_run() | + vcpu->srcu_idx = srcu_read_lock(&kvm->srcu); + r = vcpu_enter_guest(vcpu); | + kvm_vcpu_reload_apic_access_page(vcpu);
So according to backtrace I think we should fix as follows:
kvm: x86: vmx: hold kvm->srcu while reload apic access page
kvm_vcpu_reload_apic_access_page() needs to access memslots via gfn_to_page(), so its necessary to hold kvm->srcu.
Signed-off-by: Tiejun Chen <tiejun.chen@intel.com> --- arch/x86/kvm/vmx.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index b25a588..9fa1f46 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -4442,6 +4442,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu) { struct vcpu_vmx *vmx = to_vmx(vcpu); struct msr_data apic_base_msr; + int idx;
vmx->rmode.vm86_active = 0;
@@ -4509,7 +4510,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu) vmcs_write32(TPR_THRESHOLD, 0); }
+ idx = srcu_read_lock(&vcpu->kvm->srcu); kvm_vcpu_reload_apic_access_page(vcpu); + srcu_read_unlock(&vcpu->kvm->srcu, idx);
if (vmx_vm_has_apicv(vcpu->kvm)) memset(&vmx->pi_desc, 0, sizeof(struct pi_desc)); -- 1.9.1 Thanks Tiejun > page = gfn_to_page(vcpu->kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT); > + srcu_read_unlock(&vcpu->kvm->srcu, idx); > kvm_x86_ops->set_apic_access_page_addr(vcpu, page_to_phys(page)); > > /* >
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