Date: Thu, 12 Nov 2020 21:18:59 -0800 From: Brian Buhrow <buhrow@nfbcal.org> To: Roger Pau =?utf-8?B?TW9ubsOp?= <roger.pau@citrix.com> Cc: <freebsd-xen@freebsd.org>, buhrow@nfbcal.org Subject: Re: ZFS corruption using zvols as backingstore for hvm VM's Message-ID: <202011130518.0AD5IxtF013960@nfbcal.org> In-Reply-To: <20201111095009.6lcik5y3s7wrsh5k@Air-de-Roger>
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hello Roger. thanks for engaging with me on this issue. I think I've made progress on the issue and have a better handle on what's going wrong. There seem to be a cascade of bugs here, which I'll try to enumerate. 1. The disk corruption issue seems to be a bug in qemu whereby the emulated IDE disk controller issues partial writes instead of full writes or no writes with appropriate failure to the disk. The IDE driver in NetBSD-5.2 doesn't play well with this behavior, in fact, NetBSD until May of 2020, doesn't play well with this behavior See: http://mail-index.NetBSD.org/source-changes/2020/05/24/msg117668.html 2. This causes memory corruption in the OS itself, which can trigger a xen server crash! (In my view, no matter how badly behaved the guest OS is, it shouldn't be able to bring down the xen server.) 3. Running NetBSD-5.2/i386 as a domu, which works flawlessly under xen3, gets a panic: HYPERVISOR_mmu_update failed I suspect this can be worked around using some of the command line options under Xen, xpti=true,domu=false, perhaps? Are there others I should consider? If I can get the domu kernel working, or can back port the patch listed in bug 1 above, I should be off to the races. Still, I think there's a serious issue here in bug 2, listed above that ought to be looked at. Unfortunately, I don't hav a way to readily reproduce it. Any thoughts on how to achieve pv32 backward compatibility with xen3 would be greatly appreciated. Pv64 NetBSD-5.2 seems to work fine. -thanks -Brian
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