linux-kernel - Re: [PATCH 2/2] xen: reset legacy rtc flag for PV domU

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Date:   Wed, 8 Sep 2021 10:54:07 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] xen: reset legacy rtc flag for PV domU


On 9/3/21 4:49 AM, Juergen Gross wrote:
> A Xen PV guest doesn't have a legacy RTC device, so reset the legacy
> RTC flag. Otherwise the following WARN splat will occur at boot:
>
> [    1.333404] WARNING: CPU: 1 PID: 1 at /home/gross/linux/head/drivers/rtc/rtc-mc146818-lib.c:25 mc146818_get_time+0x1be/0x210
> [    1.333404] Modules linked in:
> [    1.333404] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W         5.14.0-rc7-default+ #282
> [    1.333404] RIP: e030:mc146818_get_time+0x1be/0x210
> [    1.333404] Code: c0 64 01 c5 83 fd 45 89 6b 14 7f 06 83 c5 64 89 6b 14 41 83 ec 01 b8 02 00 00 00 44 89 63 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <0f> 0b 48 c7 c7 30 0e ef 82 4c 89 e6 e8 71 2a 24 00 48 c7 c0 ff ff
> [    1.333404] RSP: e02b:ffffc90040093df8 EFLAGS: 00010002
> [    1.333404] RAX: 00000000000000ff RBX: ffffc90040093e34 RCX: 0000000000000000
> [    1.333404] RDX: 0000000000000001 RSI: 0000000000000000 RDI: 000000000000000d
> [    1.333404] RBP: ffffffff82ef0e30 R08: ffff888005013e60 R09: 0000000000000000
> [    1.333404] R10: ffffffff82373e9b R11: 0000000000033080 R12: 0000000000000200
> [    1.333404] R13: 0000000000000000 R14: 0000000000000002 R15: ffffffff82cdc6d4
> [    1.333404] FS:  0000000000000000(0000) GS:ffff88807d440000(0000) knlGS:0000000000000000
> [    1.333404] CS:  10000e030 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    1.333404] CR2: 0000000000000000 CR3: 000000000260a000 CR4: 0000000000050660
> [    1.333404] Call Trace:
> [    1.333404]  ? wakeup_sources_sysfs_init+0x30/0x30
> [    1.333404]  ? rdinit_setup+0x2b/0x2b
> [    1.333404]  early_resume_init+0x23/0xa4
> [    1.333404]  ? cn_proc_init+0x36/0x36
> [    1.333404]  do_one_initcall+0x3e/0x200
> [    1.333404]  kernel_init_freeable+0x232/0x28e
> [    1.333404]  ? rest_init+0xd0/0xd0
> [    1.333404]  kernel_init+0x16/0x120
> [    1.333404]  ret_from_fork+0x1f/0x30
>
> Cc: <stable@...r.kernel.org>
> Signed-off-by: Juergen Gross <jgross@...e.com>


Fixes: 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs") ?


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>