From: Benjamin Gilbert <bgilbert@redhat.com>
To: Wei Huang <wei@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
x86@kernel.org, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, hpa@zytor.com, linux-kernel@vger.kernel.org,
linux-x86_64@vger.kernel.org
Subject: Re: [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode
Date: Mon, 7 Jan 2019 16:53:18 -0500 [thread overview]
Message-ID: <20190107215318.GA22396@trogon.sfo.coreos.systems> (raw)
In-Reply-To: <6899e645-9579-f599-922a-eb26fc56e8ab@redhat.com>
On Mon, Jan 07, 2019 at 02:03:15PM -0600, Wei Huang wrote:
> On 1/7/19 2:25 AM, Kirill A. Shutemov wrote:
> > On Fri, Jan 04, 2019 at 05:44:11AM +0000, Wei Huang wrote:
> >> In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM
> >> when the hypervsior detects guest sets CR0.PG to 0. This causes guest OS
> >> to reboot when it tries to return from 32-bit trampoline code because CPU
> >> is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but EFER.LME=0.
> >> As a precaution, this patch sets EFER.LME=1 as part of long mode
> >> activation procedure. This extra step won't cause any harm when Linux is
> >> booting on bare-metal machine.
> >>
> >> Signed-off-by: Wei Huang <wei@redhat.com>
> >
> > Thanks for tracking this down.
>
> BTW I think this patch _might_ be related the recent reboot issue
> reported in https://lkml.org/lkml/2018/7/1/836 since the symptoms are
> exactly the same.
The problem in that case turned out to be https://lkml.org/lkml/2018/7/4/723
which was fixed by d503ac531a.
--Benjamin Gilbert
next prev parent reply other threads:[~2019-01-07 21:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190104054411.12489-1-wei@redhat.com>
[not found] ` <20190107082512.w5gkbebsypionyey@black.fi.intel.com>
2019-01-07 20:03 ` [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode Wei Huang
2019-01-07 21:53 ` Benjamin Gilbert [this message]
2019-01-07 22:02 ` Wei Huang
2019-01-29 21:03 ` [tip:x86/urgent] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline " tip-bot for Wei Huang
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