From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Borislav Petkov <bp@alien8.de>
Cc: Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Isaku Yamahata <isaku.yamahata@intel.com>,
x86@kernel.org, linux-coco@lists.linux.dev,
kexec@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] x86/kexec: Preserve CR4.MCE during kexec
Date: Thu, 16 Feb 2023 19:46:48 +0000 [thread overview]
Message-ID: <1144340e-dd95-ee3b-dabb-579f9a65b3c7@citrix.com> (raw)
In-Reply-To: <20230213234836.3683-2-kirill.shutemov@linux.intel.com>
On 13/02/2023 11:48 pm, Kirill A. Shutemov wrote:
> TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
> to #VE.
>
> Preserve the flag during kexec.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
That's unfortunate for TDX, but in a non-TDX system you must never
maintain CR4.MCE into kexec.
Async events, including NMIs, cannot be taken between this point and the
target having set itself up into it's intended operating mode. During
this period you get all kinds of fun with type confusion in the IDT/TSS
and/or not having a safe stack to service the event.
A clean shutdown from not having machine checks enabled is far
preferable to trying to deliver an #MC in purgatory.
That, or you're welcome to debug the next bug report I get where
(amazingly) an NMI managed to hit with a good stack in the new context,
but most of the old context (IDT, TSS and .text) still intact enough to
start emitting a very confused oops onto serial...
~Andrew
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next prev parent reply other threads:[~2023-02-16 19:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-13 23:48 [PATCH 0/2] Kexec enabling in TDX guest Kirill A. Shutemov
2023-02-13 23:48 ` [PATCH 1/2] x86/kexec: Preserve CR4.MCE during kexec Kirill A. Shutemov
2023-02-16 1:49 ` Edgecombe, Rick P
2023-02-16 9:43 ` Kirill A. Shutemov
2023-02-16 17:33 ` Edgecombe, Rick P
2023-02-16 19:46 ` Andrew Cooper [this message]
2023-02-13 23:48 ` [PATCH 2/2] x86/tdx: Convert shared memory back to private on kexec Kirill A. Shutemov
2023-02-15 1:53 ` Huang, Kai
2023-02-16 17:50 ` [PATCH 0/2] Kexec enabling in TDX guest Dave Hansen
2023-02-16 18:12 ` Kirill A. Shutemov
2023-02-16 18:32 ` Dave Hansen
2023-02-22 10:26 ` David Woodhouse
2023-02-24 14:30 ` Kirill A. Shutemov
2023-02-24 15:22 ` Dave Hansen
2023-02-24 16:12 ` Kirill A. Shutemov
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