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Re: [PATCH] x86/kexec: Fix kexec-reboot with CET active
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 8 Mar 2022 17:48:18 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, David Vrabel <dvrabel@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 08 Mar 2022 16:48:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.03.2022 17:22, Andrew Cooper wrote:
> On 08/03/2022 08:15, Jan Beulich wrote:
>> On 07.03.2022 21:53, Andrew Cooper wrote:
>>> --- a/xen/arch/x86/machine_kexec.c
>>> +++ b/xen/arch/x86/machine_kexec.c
>>> @@ -156,6 +156,16 @@ void machine_kexec(struct kexec_image *image)
>>> */
>>> local_irq_disable();
>>>
>>> + /* Reset CPUID masking and faulting to the host's default. */
>>> + ctxt_switch_levelling(NULL);
>>> +
>>> + /* Disable CET. */
>>> + if ( read_cr4() & X86_CR4_CET )
>>> + {
>>> + wrmsrl(MSR_S_CET, 0);
>>> + write_cr4(read_cr4() & ~X86_CR4_CET);
>>> + }
>>> +
>>> /* Now regular interrupts are disabled, we need to reduce the impact
>>> * of interrupts not disabled by 'cli'.
>>> *
>> Besides introducing somewhat of a disconnect between the comment in
>> context here and the earlier local_irq_disable(), is it really
>> necessary to do both actions with IRQs off?
>
> We are a handful of instructions away from discarding Xen's context
> entirely. IRQs are not a relevant concern.
Well, as said - the comment was what caught my eye. But as you appear to
think that slight disconnect is not an issue: I don't mean my remark to
be an objection. Feel free to commit with David's R-b.
Jan
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