From: Wei Liu <wei.liu@kernel.org>
To: Michael Kelley <mikelley@microsoft.com>
Cc: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org,
decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
peterz@infradead.org, x86@kernel.org,
linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH v2 1/1] x86/hyperv: Disable IBT when hypercall page lacks ENDBR instruction
Date: Sun, 23 Jul 2023 23:08:06 +0000 [thread overview]
Message-ID: <ZL2y1oaObNrnMHE8@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <1690001476-98594-1-git-send-email-mikelley@microsoft.com>
On Fri, Jul 21, 2023 at 09:51:16PM -0700, Michael Kelley wrote:
> On hardware that supports Indirect Branch Tracking (IBT), Hyper-V VMs
> with ConfigVersion 9.3 or later support IBT in the guest. However,
> current versions of Hyper-V have a bug in that there's not an ENDBR64
> instruction at the beginning of the hypercall page. Since hypercalls are
> made with an indirect call to the hypercall page, all hypercall attempts
> fail with an exception and Linux panics.
>
> A Hyper-V fix is in progress to add ENDBR64. But guard against the Linux
> panic by clearing X86_FEATURE_IBT if the hypercall page doesn't start
> with ENDBR. The VM will boot and run without IBT.
>
> If future Linux 32-bit kernels were to support IBT, additional hypercall
> page hackery would be needed to make IBT work for such kernels in a
> Hyper-V VM.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Applied to hyperv-fixes. Thanks.
next prev parent reply other threads:[~2023-07-23 23:08 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-22 4:51 [PATCH v2 1/1] x86/hyperv: Disable IBT when hypercall page lacks ENDBR instruction Michael Kelley
2023-07-23 23:08 ` Wei Liu [this message]
2023-07-24 21:06 ` Peter Zijlstra
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