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RE: [PATCH v3 6/7] xen/mem_access: wrap memory access when VM_EVENT=n
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: "Penny, Zheng" <penny.zheng@xxxxxxx>
- Date: Mon, 1 Dec 2025 03:46:48 +0000
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- Cc: "Huang, Ray" <Ray.Huang@xxxxxxx>, "grygorii_strashko@xxxxxxxx" <grygorii_strashko@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, Alexandru Isaila <aisaila@xxxxxxxxxxxxxxx>, Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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- Thread-topic: [PATCH v3 6/7] xen/mem_access: wrap memory access when VM_EVENT=n
[Public]
> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Monday, November 24, 2025 10:10 PM
> To: Penny, Zheng <penny.zheng@xxxxxxx>
> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; grygorii_strashko@xxxxxxxx; Andrew
> Cooper <andrew.cooper3@xxxxxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>;
> Tamas K Lengyel <tamas@xxxxxxxxxxxxx>; Alexandru Isaila
> <aisaila@xxxxxxxxxxxxxxx>; Petre Pircalabu <ppircalabu@xxxxxxxxxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v3 6/7] xen/mem_access: wrap memory access when
> VM_EVENT=n
>
> On 21.11.2025 10:15, Penny Zheng wrote:
> > @@ -2080,7 +2081,11 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
> > unsigned long gla, #endif
> > }
> >
> > - if ( req_ptr )
> > + /*
> > + * Excessive condition is to avoid runtime undefined error only
> > + * when CONFIG_USBAN=y
> > + */
> > + if ( req_ptr && vm_event_is_enabled(curr) )
> > {
>
> I fear the comment isn't really helpful this way. What's "excessive" here may
> be
> clear from patch context, but it won't be clear when looking at the code
> later. Nor
> would it then be immediately clear why the vm_event_is_enabled() check is
> (seemingly) unnecessary. How about this:
>
> "req_ptr being constant NULL when !CONFIG_VM_EVENT, CONFIG_UBSAN=y
> builds have been observed to still hit undefined-ness at runtime. Hence do a
> seemingly redundant vm_event_is_enabled() check here."
>
> With this or any other suitable improvement to the comment:
> Acked-by: Jan Beulich <jbeulich@xxxxxxxx> If we want to go with the suggestion
> above, I'd be happy to do the replacement while committing. But of course
> first the
> necessary 2nd ack will want collecting.
Thx!
>
> Jan
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