From: Gavin Shan <gshan@redhat.com>
To: Andrew Jones <andrew.jones@linux.dev>
Cc: kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kselftest@vger.kernel.org, peterx@redhat.com,
pbonzini@redhat.com, corbet@lwn.net, maz@kernel.org,
james.morse@arm.com, alexandru.elisei@arm.com,
suzuki.poulose@arm.com, oliver.upton@linux.dev,
catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org,
seanjc@google.com, drjones@redhat.com, dmatlack@google.com,
bgardon@google.com, ricarkol@google.com, zhenyzha@redhat.com,
shan.gavin@gmail.com
Subject: Re: [PATCH v1 3/5] KVM: selftests: Dirty host pages in dirty_log_test
Date: Tue, 23 Aug 2022 13:09:28 +1000 [thread overview]
Message-ID: <0496fe72-e3da-9778-b307-eb5cc157e8fe@redhat.com> (raw)
In-Reply-To: <3abb690f-e616-630f-ba40-e590ec8bb5c1@redhat.com>
Hi Drew,
On 8/22/22 4:29 PM, Gavin Shan wrote:
> On 8/19/22 3:28 PM, Andrew Jones wrote:
>> On Fri, Aug 19, 2022 at 08:55:59AM +0800, Gavin Shan wrote:
>>> It's assumed that 1024 host pages, instead of guest pages, are dirtied
>>> in each iteration in guest_code(). The current implementation misses
>>> the case of mismatched page sizes in host and guest. For example,
>>> ARM64 could have 64KB page size in guest, but 4KB page size in host.
>>> (TEST_PAGES_PER_LOOP / 16), instead of TEST_PAGES_PER_LOOP, host pages
>>> are dirtied in every iteration.
>>>
>>> Fix the issue by touching all sub-pages when we have mismatched
>>> page sizes in host and guest.
>>
>> I'll let the dirty-log test authors decide what's best to do for this
>> test, but I'd think we should let the guest continue dirtying its
>> pages without knowledge of the host pages. Then, adjust the host test
>> code to assert all sub-pages, other than the ones it expects the guest
>> to have written, remain untouched.
>>
>
> I don't think what is clarified in the change log is correct. The current
> implementation already had the logic to handle the mismatched page sizes
> in vm_dirty_log_verify() where 'step' is used for it by fetching value
> from vm_num_host_pages(mode, 1). Please ignore this patch for now, as
> explained below.
>
> The issue I have is the 'dirty_log_test' hangs when I have 4KB host page size
> and 64KB guest page size. It seems the vcpu doesn't exit due to full ring
> buffer state or kick-off. I will have more investigations to figure out the
> root cause.
>
[...]
Please ignore this PATCH[3/5], I think this should be fixed by selecting
correct dirty ring count and the fix will be folded to PATCH[5/5] in next
revision.
In dirty_log_test, we have 1GB memory for guest to write and make them
dirty. When we have mismatch page sizes on host and guest, which is either
4kb-host-64kb-guest or 64kb-host-4kb-guest apart from 16kb case, 16384 host
pages are dirtied in each iteration. The default dirty ring count is 65536.
So the vcpu never exit due to full-dirty-ring-buffer state. This leads the
guest's code keep running and the dirty log isn't collected by the main
thread.
#define TEST_DIRTY_RING_COUNT 65536
dirty_pages_per_iteration = (0x40000000 / 0x10000)
= 0x4000
= 16384
Thanks,
Gavin
next prev parent reply other threads:[~2022-08-23 3:11 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-19 0:55 [PATCH v1 0/5] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-08-19 0:55 ` [PATCH v1 1/5] " Gavin Shan
2022-08-19 8:00 ` Marc Zyngier
2022-08-22 1:58 ` Gavin Shan
2022-08-22 18:55 ` Peter Xu
2022-08-23 3:19 ` Gavin Shan
2022-08-22 21:42 ` Marc Zyngier
2022-08-23 5:22 ` Gavin Shan
2022-08-23 13:58 ` Peter Xu
2022-08-23 19:17 ` Marc Zyngier
2022-08-23 21:20 ` Peter Xu
2022-08-23 22:47 ` Marc Zyngier
2022-08-23 23:19 ` Peter Xu
2022-08-24 14:45 ` Marc Zyngier
2022-08-24 16:21 ` Peter Xu
2022-08-24 20:57 ` Marc Zyngier
2022-08-26 6:05 ` Gavin Shan
2022-08-26 10:50 ` Paolo Bonzini
2022-08-26 15:49 ` Marc Zyngier
2022-08-27 8:27 ` Paolo Bonzini
2022-08-23 14:44 ` Oliver Upton
2022-08-23 20:35 ` Marc Zyngier
2022-08-26 10:58 ` Paolo Bonzini
2022-08-26 15:28 ` Marc Zyngier
2022-08-30 14:42 ` Peter Xu
2022-09-02 0:19 ` Paolo Bonzini
2022-08-19 0:55 ` [PATCH v1 2/5] KVM: selftests: Use host page size to map ring buffer in dirty_log_test Gavin Shan
2022-08-19 0:55 ` [PATCH v1 3/5] KVM: selftests: Dirty host pages " Gavin Shan
2022-08-19 5:28 ` Andrew Jones
2022-08-22 6:29 ` Gavin Shan
2022-08-23 3:09 ` Gavin Shan [this message]
2022-08-19 0:56 ` [PATCH v1 4/5] KVM: selftests: Clear dirty ring states between two modes " Gavin Shan
2022-08-19 0:56 ` [PATCH v1 5/5] KVM: selftests: Automate choosing dirty ring size " Gavin Shan
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