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Message-Id: <1496914224-87730-1-git-send-email-wanpeng.li@hotmail.com>
Date: Thu, 8 Jun 2017 02:30:24 -0700
From: Wanpeng Li <kernellwp@...il.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Wanpeng Li <wanpeng.li@...mail.com>
Subject: [PATCH RFC] KVM: async_pf: fix async_pf exception injection
INFO: task gnome-terminal-:1734 blocked for more than 120 seconds.
Not tainted 4.12.0-rc4+ #8
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
gnome-terminal- D 0 1734 1015 0x00000000
Call Trace:
__schedule+0x3cd/0xb30
schedule+0x40/0x90
kvm_async_pf_task_wait+0x1cc/0x270
? __vfs_read+0x37/0x150
? prepare_to_swait+0x22/0x70
do_async_page_fault+0x77/0xb0
? do_async_page_fault+0x77/0xb0
async_page_fault+0x28/0x30
This is triggered by running both win7 and win2016 on L1 KVM simultaneously,
and then gives stress to memory on L1, I can observed this hang on L1 when
at least ~70% swap area is occupied on L0.
This is due to async pf was injected to L2 which should be injected to L1,
L2 guest starts receiving pagefault w/ bogus %cr2(apf token from the host
actually), and L1 guest starts accumulating tasks stuck in D state in
kvm_async_pf_task_wait().
I try to fix it according to Radim's proposal "force a nested VM exit from
nested_vmx_check_exception if the injected #PF is async_pf and handle the #PF
VM exit in L1". https://www.spinics.net/lists/kvm/msg142498.html
However, I found that "nr == PF_VECTOR && vmx->apf_reason != 0" never be true
in nested_vmx_check_exception(). SVM depends on the similar stuff in
nested_svm_intercept() which makes me confusing how it can works. In addition,
vmx/svm->apf_reason should be got in L1 since apf_reason.reason will make sense
just in pv guest. So vmx/svm->apf_reason should always be 0 on L0. I change the
condition to "nr == PF_VECTOR && error_code == 0" to intercept async_pf, however,
the below bug will be splatted:
BUG: unable to handle kernel paging request at ffffe305770a87e0
IP: kfree+0x6f/0x300
PGD 0
P4D 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 3 PID: 2187 Comm: transhuge-stres Tainted: G OE 4.12.0-rc4+ #9
task: ffff8a9214b58000 task.stack: ffffb46bc34e4000
RIP: 0010:kfree+0x6f/0x300
RSP: 0000:ffffb46bc34e7b28 EFLAGS: 00010086
RAX: ffffe305770a87c0 RBX: ffffb46bc2a1fe70 RCX: 0000000000000001
RDX: 0000757180000000 RSI: 00000000ffffffff RDI: 0000000000000096
RBP: ffffb46bc34e7b50 R08: 0000000000000000 R09: 0000000000000001
R10: ffffb46bc34e7ac8 R11: 68b9962a00000000 R12: 000000a7770a87c0
R13: ffffffff90059b75 R14: ffffffff913466c0 R15: ffffe25e06f18000
FS: 00007f1904ae7700(0000) GS:ffff8a921a800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffe305770a87e0 CR3: 000000040eb5c000 CR4: 00000000001426e0
Call Trace:
kvm_async_pf_task_wait+0xd5/0x280
? __this_cpu_preempt_check+0x13/0x20
do_async_page_fault+0x77/0xb0
? do_async_page_fault+0x77/0xb0
async_page_fault+0x28/0x30
In additon, if svm->apf_reason doen't make sense on L0, then maybe it also will not
work in the function nested_svm_exit_special().
The patch below is uncompleted, and your inputs to improve it is a great appreciated.
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
arch/x86/kvm/vmx.c | 41 ++++++++++++++++++++++++++++++++---------
1 file changed, 32 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ca5d2b9..21a1b44 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -616,6 +616,7 @@ struct vcpu_vmx {
bool emulation_required;
u32 exit_reason;
+ u32 apf_reason;
/* Posted interrupt descriptor */
struct pi_desc pi_desc;
@@ -2418,11 +2419,12 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
* KVM wants to inject page-faults which it got to the guest. This function
* checks whether in a nested guest, we need to inject them to L1 or L2.
*/
-static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned nr)
+static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
{
struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
- if (!(vmcs12->exception_bitmap & (1u << nr)))
+ if (!((vmcs12->exception_bitmap & (1u << nr)) ||
+ (nr == PF_VECTOR && error_code == 0)))
return 0;
nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI,
@@ -2439,7 +2441,7 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu, unsigned nr,
u32 intr_info = nr | INTR_INFO_VALID_MASK;
if (!reinject && is_guest_mode(vcpu) &&
- nested_vmx_check_exception(vcpu, nr))
+ nested_vmx_check_exception(vcpu, nr, error_code))
return;
if (has_error_code) {
@@ -5646,14 +5648,31 @@ static int handle_exception(struct kvm_vcpu *vcpu)
}
if (is_page_fault(intr_info)) {
- /* EPT won't cause page fault directly */
- BUG_ON(enable_ept);
cr2 = vmcs_readl(EXIT_QUALIFICATION);
- trace_kvm_page_fault(cr2, error_code);
+ switch (vmx->apf_reason) {
+ default:
+ /* EPT won't cause page fault directly */
+ BUG_ON(enable_ept);
+ trace_kvm_page_fault(cr2, error_code);
- if (kvm_event_needs_reinjection(vcpu))
- kvm_mmu_unprotect_page_virt(vcpu, cr2);
- return kvm_mmu_page_fault(vcpu, cr2, error_code, NULL, 0);
+ if (kvm_event_needs_reinjection(vcpu))
+ kvm_mmu_unprotect_page_virt(vcpu, cr2);
+ return kvm_mmu_page_fault(vcpu, cr2, error_code, NULL, 0);
+ break;
+ case KVM_PV_REASON_PAGE_NOT_PRESENT:
+ vmx->apf_reason = 0;
+ local_irq_disable();
+ kvm_async_pf_task_wait(cr2);
+ local_irq_enable();
+ break;
+ case KVM_PV_REASON_PAGE_READY:
+ vmx->apf_reason = 0;
+ local_irq_disable();
+ kvm_async_pf_task_wake(cr2);
+ local_irq_enable();
+ break;
+ }
+ return 0;
}
ex_no = intr_info & INTR_INFO_VECTOR_MASK;
@@ -8600,6 +8619,10 @@ static void vmx_complete_atomic_exit(struct vcpu_vmx *vmx)
vmx->exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
exit_intr_info = vmx->exit_intr_info;
+ /* if exit due to PF check for async PF */
+ if (is_page_fault(exit_intr_info))
+ vmx->apf_reason = kvm_read_and_reset_pf_reason();
+
/* Handle machine checks before interrupts are enabled */
if (is_machine_check(exit_intr_info))
kvm_machine_check();
--
2.7.4
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