Re: KVM Test result, kernel ff5bdac.., userspace eb2fd67.. -- OneNew Issue

Yunfeng Zhao
2008-06-12T09:25:56Z

> On Fri, Jun 06, 2008 at 11:11:12AM +0800, Yunfeng Zhao wrote:
>
>> Hi All,
>>
>> This is today's KVM test result against kvm.git
>> ff5bdac4be0230e0bb33e4208ac0a91343c72929 and kvm-userspace.git
>> eb2fd67cbecdb573f908697ed41b81ee312372bd.
>>
>> One New Issue:
>> ================================================
>> 1. Guests crash while rebooting
>> https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1976075&group_id=180599
>>
>>
>> Five Old Issues:
>> ================================================
>> 2. Fail to save restore and live migrate
>> https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1976075&group_id=180599
>> 3. netperf causes linux guest with virtnet kernel panic
>> https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1972449&group_id=180599
>> 4. XP crashes while rebooting
>> https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1959452&group_id=180599
>> 5.Cannot boot guests with hugetlbfs
>> https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1941302&group_id=180599
>>
>
> This is a get_user_pages() with hugetlb-vma's bug, not KVM's problem,
> fixed by:
>
> commit 5b23dbe8173c212d6a326e35347b038705603d39
> Author: Adam Litke <agl@us.ibm.com>
> Date: Wed Nov 14 16:59:33 2007 -0800
>
> hugetlb: follow_hugetlb_page() for write access
>
> When calling get_user_pages(), a write flag is passed in by the caller to
> indicate if write access is required on the faulted-in pages.
>
> Currently, follow_hugetlb_page() ignores this flag and always faults pages for
> read-only access. This can cause data corruption because a device driver
> that calls get_user_pages() with write set will not expect COW faults to
> occur on the returned pages.
>
> This patch passes the write flag down to follow_hugetlb_page() and makes
> sure hugetlb_fault() is called with the right write_access parameter.
>
> Can you please upgrade your test hosts to 2.6.25 or newer?
>
I tried to test it against 2.6.25-rc5.
The host hanged while booting a xp guest.

Thanks
Yunfeng
> Perhaps kvm-userspace should check for kernel version and disable
> hugetlb backed memory. Nasty.
>
> Thanks John for help in tracking this down.
>
>