From: "H. Peter Anvin" <hpa@zytor.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Baoquan He <bhe@redhat.com>,
x86@kernel.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@kernel.org, kirill.shutemov@linux.intel.com
Subject: Re: [PATCH 1/3] x86/boot: Add bit fields into xloadflags for 5-level kernel checking
Date: Tue, 4 Sep 2018 21:06:07 -0700 [thread overview]
Message-ID: <7a1147d7-05af-98fe-3a14-b18ea445c2b5@zytor.com> (raw)
In-Reply-To: <20180904084231.ubyjaqp4xhqcnper@kshutemo-mobl1>
On 09/04/18 01:42, Kirill A. Shutemov wrote:
>
> Switching between 4- and 5-level paging modes (in either direction)
> requires paing disabling. It means the code that does the switching has to
> be under 4G otherwise we would lose control.
>
> We handle the switching correctly in kernel decompression code, but not on
> kexec caller side.
>
> XLF_5LEVEL indicates that kernel decompression code can deal with
> switching between paging modes and it's safe to jump there in 5-level
> paging mode.
>
> As an alternative we can change kexec to switch to 4-level paging mode
> before starting the new kernel. Not sure how hard it will be.
>
Have a flag saying entering in 5-level mode is fine. However, you really
should support returning to 4-level mode in kexec. It is *much* easier to do
on the caller side as you have total control of memory allocation there.
-hpa
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next prev parent reply other threads:[~2018-09-05 4:06 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-29 14:16 [PATCH 0/3] Add restrictions for kexec/kdump jumping between 5-level and 4-level kernel Baoquan He
2018-08-29 14:16 ` [PATCH 1/3] x86/boot: Add bit fields into xloadflags for 5-level kernel checking Baoquan He
2018-09-04 2:41 ` H. Peter Anvin
2018-09-04 3:44 ` Baoquan He
2018-09-04 4:13 ` H. Peter Anvin
2018-09-04 5:20 ` Baoquan He
2018-09-04 5:46 ` H. Peter Anvin
2018-09-04 6:06 ` Baoquan He
2018-09-04 6:36 ` H. Peter Anvin
2018-09-04 7:16 ` Baoquan He
2018-09-04 8:42 ` Kirill A. Shutemov
2018-09-05 4:06 ` H. Peter Anvin [this message]
2018-09-05 8:02 ` Thomas Gleixner
2018-09-26 7:54 ` Baoquan He
2018-08-29 14:16 ` [PATCH 2/3] x86/kexec/64: Error out if try to jump to old 4-level kernel from 5-level kernel Baoquan He
2018-08-29 14:16 ` [PATCH 3/3] x86/kdump/64: Change the upper limit of crashkernel reservation Baoquan He
2018-08-30 13:50 ` Kirill A. Shutemov
2018-08-30 14:13 ` Baoquan He
2018-08-30 13:58 ` [PATCH 0/3] Add restrictions for kexec/kdump jumping between 5-level and 4-level kernel Kirill A. Shutemov
2018-08-30 14:12 ` Baoquan He
2018-08-30 14:27 ` Kirill A. Shutemov
2018-08-30 14:57 ` Baoquan He
2018-08-30 15:01 ` Baoquan He
2018-09-02 20:45 ` Kirill A. Shutemov
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