| Message ID | 20220222031239.1076682-1-zhangliang5@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RESEND] KVM: x86/mmu: make apf token non-zero to fix bug | expand |
On 2/22/22 04:12, Liang Zhang wrote: > In current async pagefault logic, when a page is ready, KVM relies on > kvm_arch_can_dequeue_async_page_present() to determine whether to deliver > a READY event to the Guest. This function test token value of struct > kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a > READY event is finished by Guest. If value is zero meaning that a READY > event is done, so the KVM can deliver another. > But the kvm_arch_setup_async_pf() may produce a valid token with zero > value, which is confused with previous mention and may lead the loss of > this READY event. > > This bug may cause task blocked forever in Guest: > INFO: task stress:7532 blocked for more than 1254 seconds. > Not tainted 5.10.0 #16 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:stress state:D stack: 0 pid: 7532 ppid: 1409 > flags:0x00000080 > Call Trace: > __schedule+0x1e7/0x650 > schedule+0x46/0xb0 > kvm_async_pf_task_wait_schedule+0xad/0xe0 > ? exit_to_user_mode_prepare+0x60/0x70 > __kvm_handle_async_pf+0x4f/0xb0 > ? asm_exc_page_fault+0x8/0x30 > exc_page_fault+0x6f/0x110 > ? asm_exc_page_fault+0x8/0x30 > asm_exc_page_fault+0x1e/0x30 > RIP: 0033:0x402d00 > RSP: 002b:00007ffd31912500 EFLAGS: 00010206 > RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0 > RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0 > RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086 > R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000 > R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000 > > Signed-off-by: Liang Zhang <zhangliang5@huawei.com> > --- > arch/x86/kvm/mmu/mmu.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 593093b52395..8e24f73bf60b 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3889,12 +3889,23 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr) > walk_shadow_page_lockless_end(vcpu); > } > > +static u32 alloc_apf_token(struct kvm_vcpu *vcpu) > +{ > + /* make sure the token value is not 0 */ > + u32 id = vcpu->arch.apf.id; > + > + if (id << 12 == 0) > + vcpu->arch.apf.id = 1; > + > + return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; > +} > + > static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > gfn_t gfn) > { > struct kvm_arch_async_pf arch; > > - arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; > + arch.token = alloc_apf_token(vcpu); > arch.gfn = gfn; > arch.direct_map = vcpu->arch.mmu->direct_map; > arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu); Queued, thanks. Paolo
On 2022/2/22 11:12, Liang Zhang wrote: > In current async pagefault logic, when a page is ready, KVM relies on > kvm_arch_can_dequeue_async_page_present() to determine whether to deliver > a READY event to the Guest. This function test token value of struct > kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a > READY event is finished by Guest. If value is zero meaning that a READY > event is done, so the KVM can deliver another. > But the kvm_arch_setup_async_pf() may produce a valid token with zero > value, which is confused with previous mention and may lead the loss of > this READY event. > > This bug may cause task blocked forever in Guest: > INFO: task stress:7532 blocked for more than 1254 seconds. > Not tainted 5.10.0 #16 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:stress state:D stack: 0 pid: 7532 ppid: 1409 > flags:0x00000080 > Call Trace: > __schedule+0x1e7/0x650 > schedule+0x46/0xb0 > kvm_async_pf_task_wait_schedule+0xad/0xe0 > ? exit_to_user_mode_prepare+0x60/0x70 > __kvm_handle_async_pf+0x4f/0xb0 > ? asm_exc_page_fault+0x8/0x30 > exc_page_fault+0x6f/0x110 > ? asm_exc_page_fault+0x8/0x30 > asm_exc_page_fault+0x1e/0x30 > RIP: 0033:0x402d00 > RSP: 002b:00007ffd31912500 EFLAGS: 00010206 > RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0 > RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0 > RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086 > R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000 > R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000 > > Signed-off-by: Liang Zhang <zhangliang5@huawei.com> > --- > arch/x86/kvm/mmu/mmu.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 593093b52395..8e24f73bf60b 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -3889,12 +3889,23 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr) > walk_shadow_page_lockless_end(vcpu); > } > > +static u32 alloc_apf_token(struct kvm_vcpu *vcpu) > +{ > + /* make sure the token value is not 0 */ > + u32 id = vcpu->arch.apf.id; > + > + if (id << 12 == 0) > + vcpu->arch.apf.id = 1; > + > + return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; > +} > + > static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, > gfn_t gfn) > { > struct kvm_arch_async_pf arch; > > - arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; This patch is completely OK. But I have a question, can we simplify it to arch.token = (++vcpu->arch.apf.id << 12) | vcpu->vcpu_id; > + arch.token = alloc_apf_token(vcpu); > arch.gfn = gfn; > arch.direct_map = vcpu->arch.mmu->direct_map; > arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu);
No. Because '(++vcpu->arch.apf.id << 12)' may also produce zero value. On 2022/3/10 11:34, Xinlong Lin wrote: > > > On 2022/2/22 11:12, Liang Zhang wrote: >> In current async pagefault logic, when a page is ready, KVM relies on >> kvm_arch_can_dequeue_async_page_present() to determine whether to deliver >> a READY event to the Guest. This function test token value of struct >> kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a >> READY event is finished by Guest. If value is zero meaning that a READY >> event is done, so the KVM can deliver another. >> But the kvm_arch_setup_async_pf() may produce a valid token with zero >> value, which is confused with previous mention and may lead the loss of >> this READY event. >> >> This bug may cause task blocked forever in Guest: >> INFO: task stress:7532 blocked for more than 1254 seconds. >> Not tainted 5.10.0 #16 >> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >> task:stress state:D stack: 0 pid: 7532 ppid: 1409 >> flags:0x00000080 >> Call Trace: >> __schedule+0x1e7/0x650 >> schedule+0x46/0xb0 >> kvm_async_pf_task_wait_schedule+0xad/0xe0 >> ? exit_to_user_mode_prepare+0x60/0x70 >> __kvm_handle_async_pf+0x4f/0xb0 >> ? asm_exc_page_fault+0x8/0x30 >> exc_page_fault+0x6f/0x110 >> ? asm_exc_page_fault+0x8/0x30 >> asm_exc_page_fault+0x1e/0x30 >> RIP: 0033:0x402d00 >> RSP: 002b:00007ffd31912500 EFLAGS: 00010206 >> RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0 >> RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0 >> RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086 >> R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000 >> R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000 >> >> Signed-off-by: Liang Zhang <zhangliang5@huawei.com> >> --- >> arch/x86/kvm/mmu/mmu.c | 13 ++++++++++++- >> 1 file changed, 12 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c >> index 593093b52395..8e24f73bf60b 100644 >> --- a/arch/x86/kvm/mmu/mmu.c >> +++ b/arch/x86/kvm/mmu/mmu.c >> @@ -3889,12 +3889,23 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr) >> walk_shadow_page_lockless_end(vcpu); >> } >> +static u32 alloc_apf_token(struct kvm_vcpu *vcpu) >> +{ >> + /* make sure the token value is not 0 */ >> + u32 id = vcpu->arch.apf.id; >> + >> + if (id << 12 == 0) >> + vcpu->arch.apf.id = 1; >> + >> + return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; >> +} >> + >> static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, >> gfn_t gfn) >> { >> struct kvm_arch_async_pf arch; >> - arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; > This patch is completely OK. But I have a question, can we simplify it to > arch.token = (++vcpu->arch.apf.id << 12) | vcpu->vcpu_id; >> + arch.token = alloc_apf_token(vcpu); >> arch.gfn = gfn; >> arch.direct_map = vcpu->arch.mmu->direct_map; >> arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu); > > .
Thank you and sorry for the noise. On 2022/3/10 11:42, zhangliang (AG) wrote: > No. Because '(++vcpu->arch.apf.id << 12)' may also produce zero value. > > On 2022/3/10 11:34, Xinlong Lin wrote: >> >> >> On 2022/2/22 11:12, Liang Zhang wrote: >>> In current async pagefault logic, when a page is ready, KVM relies on >>> kvm_arch_can_dequeue_async_page_present() to determine whether to deliver >>> a READY event to the Guest. This function test token value of struct >>> kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a >>> READY event is finished by Guest. If value is zero meaning that a READY >>> event is done, so the KVM can deliver another. >>> But the kvm_arch_setup_async_pf() may produce a valid token with zero >>> value, which is confused with previous mention and may lead the loss of >>> this READY event. >>> >>> This bug may cause task blocked forever in Guest: >>> INFO: task stress:7532 blocked for more than 1254 seconds. >>> Not tainted 5.10.0 #16 >>> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. >>> task:stress state:D stack: 0 pid: 7532 ppid: 1409 >>> flags:0x00000080 >>> Call Trace: >>> __schedule+0x1e7/0x650 >>> schedule+0x46/0xb0 >>> kvm_async_pf_task_wait_schedule+0xad/0xe0 >>> ? exit_to_user_mode_prepare+0x60/0x70 >>> __kvm_handle_async_pf+0x4f/0xb0 >>> ? asm_exc_page_fault+0x8/0x30 >>> exc_page_fault+0x6f/0x110 >>> ? asm_exc_page_fault+0x8/0x30 >>> asm_exc_page_fault+0x1e/0x30 >>> RIP: 0033:0x402d00 >>> RSP: 002b:00007ffd31912500 EFLAGS: 00010206 >>> RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0 >>> RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0 >>> RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086 >>> R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000 >>> R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000 >>> >>> Signed-off-by: Liang Zhang <zhangliang5@huawei.com> >>> --- >>> arch/x86/kvm/mmu/mmu.c | 13 ++++++++++++- >>> 1 file changed, 12 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c >>> index 593093b52395..8e24f73bf60b 100644 >>> --- a/arch/x86/kvm/mmu/mmu.c >>> +++ b/arch/x86/kvm/mmu/mmu.c >>> @@ -3889,12 +3889,23 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr) >>> walk_shadow_page_lockless_end(vcpu); >>> } >>> +static u32 alloc_apf_token(struct kvm_vcpu *vcpu) >>> +{ >>> + /* make sure the token value is not 0 */ >>> + u32 id = vcpu->arch.apf.id; >>> + >>> + if (id << 12 == 0) >>> + vcpu->arch.apf.id = 1; >>> + >>> + return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; >>> +} >>> + >>> static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, >>> gfn_t gfn) >>> { >>> struct kvm_arch_async_pf arch; >>> - arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; >> This patch is completely OK. But I have a question, can we simplify it to >> arch.token = (++vcpu->arch.apf.id << 12) | vcpu->vcpu_id; >>> + arch.token = alloc_apf_token(vcpu); >>> arch.gfn = gfn; >>> arch.direct_map = vcpu->arch.mmu->direct_map; >>> arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu); >> >> . >
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 593093b52395..8e24f73bf60b 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3889,12 +3889,23 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr) walk_shadow_page_lockless_end(vcpu); } +static u32 alloc_apf_token(struct kvm_vcpu *vcpu) +{ + /* make sure the token value is not 0 */ + u32 id = vcpu->arch.apf.id; + + if (id << 12 == 0) + vcpu->arch.apf.id = 1; + + return (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; +} + static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, gfn_t gfn) { struct kvm_arch_async_pf arch; - arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id; + arch.token = alloc_apf_token(vcpu); arch.gfn = gfn; arch.direct_map = vcpu->arch.mmu->direct_map; arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu);
In current async pagefault logic, when a page is ready, KVM relies on kvm_arch_can_dequeue_async_page_present() to determine whether to deliver a READY event to the Guest. This function test token value of struct kvm_vcpu_pv_apf_data, which must be reset to zero by Guest kernel when a READY event is finished by Guest. If value is zero meaning that a READY event is done, so the KVM can deliver another. But the kvm_arch_setup_async_pf() may produce a valid token with zero value, which is confused with previous mention and may lead the loss of this READY event. This bug may cause task blocked forever in Guest: INFO: task stress:7532 blocked for more than 1254 seconds. Not tainted 5.10.0 #16 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:stress state:D stack: 0 pid: 7532 ppid: 1409 flags:0x00000080 Call Trace: __schedule+0x1e7/0x650 schedule+0x46/0xb0 kvm_async_pf_task_wait_schedule+0xad/0xe0 ? exit_to_user_mode_prepare+0x60/0x70 __kvm_handle_async_pf+0x4f/0xb0 ? asm_exc_page_fault+0x8/0x30 exc_page_fault+0x6f/0x110 ? asm_exc_page_fault+0x8/0x30 asm_exc_page_fault+0x1e/0x30 RIP: 0033:0x402d00 RSP: 002b:00007ffd31912500 EFLAGS: 00010206 RAX: 0000000000071000 RBX: ffffffffffffffff RCX: 00000000021a32b0 RDX: 000000000007d011 RSI: 000000000007d000 RDI: 00000000021262b0 RBP: 00000000021262b0 R08: 0000000000000003 R09: 0000000000000086 R10: 00000000000000eb R11: 00007fefbdf2baa0 R12: 0000000000000000 R13: 0000000000000002 R14: 000000000007d000 R15: 0000000000001000 Signed-off-by: Liang Zhang <zhangliang5@huawei.com> --- arch/x86/kvm/mmu/mmu.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)