Messages in this thread | | | Subject | Re: [PATCH v1 3/5] KVM: selftests: Dirty host pages in dirty_log_test | From | Gavin Shan <> | Date | Tue, 23 Aug 2022 13:09:28 +1000 |
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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. >
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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
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