linux-kernel - Re: [PATCH 0/7] KVM: Alleviate mmu_lock hold time when we start dirty logging

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Date:	Wed, 19 Dec 2012 08:42:57 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
Cc:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>,
	mtosatti@...hat.com, gleb@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] KVM: Alleviate mmu_lock hold time when we start
 dirty logging

On Wed, 2012-12-19 at 21:30 +0900, Takuya Yoshikawa wrote:
> Ccing Alex,
> 
> I tested kvm.git next branch before Alex's patch set was applied, and
> did not see the bug.  Although I'm not 100% sure but it is possible
> that something got broken by a patch in the following series:
> 
> [01/10] KVM: Restrict non-existing slot state transitions
> [02/10] KVM: Check userspace_addr when modifying a memory slot
> [03/10] KVM: Fix iommu map/unmap to handle memory slot moves
> [04/10] KVM: Minor memory slot optimization
> [05/10] KVM: Rename KVM_MEMORY_SLOTS -> KVM_USER_MEM_SLOTS
> [06/10] KVM: Make KVM_PRIVATE_MEM_SLOTS optional
> [07/10] KVM: struct kvm_memory_slot.user_alloc -> bool
> [08/10] KVM: struct kvm_memory_slot.flags -> u32
> [09/10] KVM: struct kvm_memory_slot.id -> short
> [10/10] KVM: Increase user memory slots on x86 to 125
> 
> If I can get time, I will check which one caused the problem tomorrow.

Please let me know if you can identify one of these as the culprit.
They're all very simple, but there's always a chance I've missed a hard
coding of slot numbers somewhere.  Thanks,

Alex

> On Tue, 18 Dec 2012 16:25:58 +0900
> Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp> wrote:
> 
> > IMPORTANT NOTE (not about this patch set):
> > 
> > I have hit the following bug many times with the current next branch,
> > even WITHOUT my patches.  Although I do not know a way to reproduce this
> > yet, it seems that something was broken around slot->dirty_bitmap.  I am
> > now investigating the new code in __kvm_set_memory_region().
> > 
> > The bug:
> > [  575.238063] BUG: unable to handle kernel paging request at 00000002efe83a77
> > [  575.238185] IP: [<ffffffffa05f9619>] mark_page_dirty_in_slot+0x19/0x20 [kvm]
> > [  575.238308] PGD 0 
> > [  575.238343] Oops: 0002 [#1] SMP 
> > 
> > The call trace:
> > [  575.241207] Call Trace:
> > [  575.241257]  [<ffffffffa05f96b1>] kvm_write_guest_cached+0x91/0xb0 [kvm]
> > [  575.241370]  [<ffffffffa0610db9>] kvm_arch_vcpu_ioctl_run+0x1109/0x12c0 [kvm]
> > [  575.241488]  [<ffffffffa060fd55>] ? kvm_arch_vcpu_ioctl_run+0xa5/0x12c0 [kvm]
> > [  575.241595]  [<ffffffff81679194>] ? mutex_lock_killable_nested+0x274/0x340
> > [  575.241706]  [<ffffffffa05faf80>] ? kvm_set_ioapic_irq+0x20/0x20 [kvm]
> > [  575.241813]  [<ffffffffa05f71c9>] kvm_vcpu_ioctl+0x559/0x670 [kvm]
> > [  575.241913]  [<ffffffffa05f8a58>] ? kvm_vm_ioctl+0x1b8/0x570 [kvm]
> > [  575.242007]  [<ffffffff8101b9d3>] ? native_sched_clock+0x13/0x80
> > [  575.242125]  [<ffffffff8101ba49>] ? sched_clock+0x9/0x10
> > [  575.242208]  [<ffffffff8109015d>] ? sched_clock_cpu+0xbd/0x110
> > [  575.242298]  [<ffffffff811a914c>] ? fget_light+0x3c/0x140
> > [  575.242381]  [<ffffffff8119dfa8>] do_vfs_ioctl+0x98/0x570
> > [  575.242463]  [<ffffffff811a91b1>] ? fget_light+0xa1/0x140
> > [  575.246393]  [<ffffffff811a914c>] ? fget_light+0x3c/0x140
> > [  575.250363]  [<ffffffff8119e511>] sys_ioctl+0x91/0xb0
> > [  575.254327]  [<ffffffff81684c19>] system_call_fastpath+0x16/0x1b



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