linux-kernel - Re: [PATCH 0/2] Fix the Xen HVM kdump/kexec boot panic issue

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Date:   Tue, 12 Oct 2021 10:47:09 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        xen-devel@...ts.xenproject.org
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        boris.ostrovsky@...cle.com, sstabellini@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        andrew.cooper3@...rix.com, george.dunlap@...rix.com,
        iwj@...project.org, jbeulich@...e.com, julien@....org, wl@....org,
        joe.jin@...cle.com
Subject: Re: [PATCH 0/2] Fix the Xen HVM kdump/kexec boot panic issue

On 12.10.21 09:24, Dongli Zhang wrote:
> When the kdump/kexec is enabled at HVM VM side, to panic kernel will trap
> to xen side with reason=soft_reset. As a result, the xen will reboot the VM
> with the kdump kernel.
> 
> Unfortunately, when the VM is panic with below command line ...
> 
> "taskset -c 33 echo c > /proc/sysrq-trigger"
> 
> ... the kdump kernel is panic at early stage ...
> 
> PANIC: early exception 0x0e IP 10:ffffffffa8c66876 error 0 cr2 0x20
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 5.15.0-rc5xen #1
> [    0.000000] Hardware name: Xen HVM domU
> [    0.000000] RIP: 0010:pvclock_clocksource_read+0x6/0xb0
> ... ...
> [    0.000000] RSP: 0000:ffffffffaa203e20 EFLAGS: 00010082 ORIG_RAX: 0000000000000000
> [    0.000000] RAX: 0000000000000003 RBX: 0000000000010000 RCX: 00000000ffffdfff
> [    0.000000] RDX: 0000000000000003 RSI: 00000000ffffdfff RDI: 0000000000000020
> [    0.000000] RBP: 0000000000011000 R08: 0000000000000000 R09: 0000000000000001
> [    0.000000] R10: ffffffffaa203e00 R11: ffffffffaa203c70 R12: 0000000040000004
> [    0.000000] R13: ffffffffaa203e5c R14: ffffffffaa203e58 R15: 0000000000000000
> [    0.000000] FS:  0000000000000000(0000) GS:ffffffffaa95e000(0000) knlGS:0000000000000000
> [    0.000000] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    0.000000] CR2: 0000000000000020 CR3: 00000000ec9e0000 CR4: 00000000000406a0
> [    0.000000] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [    0.000000] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [    0.000000] Call Trace:
> [    0.000000]  ? xen_init_time_common+0x11/0x55
> [    0.000000]  ? xen_hvm_init_time_ops+0x23/0x45
> [    0.000000]  ? xen_hvm_guest_init+0x214/0x251
> [    0.000000]  ? 0xffffffffa8c00000
> [    0.000000]  ? setup_arch+0x440/0xbd6
> [    0.000000]  ? start_kernel+0x6a/0x689
> [    0.000000]  ? secondary_startup_64_no_verify+0xc2/0xcb
> 
> This is because Xen HVM supports at most MAX_VIRT_CPUS=32 'vcpu_info'
> embedded inside 'shared_info' during early stage until xen_vcpu_setup() is
> used to allocate/relocate 'vcpu_info' for boot cpu at arbitrary address.
> 
> 
> The 1st patch is to fix the issue at VM kernel side. However, we may
> observe clock drift at VM side due to the issue at xen hypervisor side.
> This is because the pv vcpu_time_info is not updated when
> VCPUOP_register_vcpu_info.
> 
> The 2nd patch is to force_update_vcpu_system_time() at xen side when
> VCPUOP_register_vcpu_info, to avoid the VM clock drift during kdump kernel
> boot.

Please don't mix patches for multiple projects in one series.

In cases like this it is fine to mention the other project's patch
verbally instead.


Juergen

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