Re: [RESEND RFC PATCH v1 1/5] arm64: Add TLB Conflict Abort Exception handler to KVM

[Ryan Roberts <ryan.roberts@arm.com>]

On 12/12/2024 09:57, Marc Zyngier wrote:
> Hi Ryan,
> 
> On Thu, 12 Dec 2024 09:23:20 +0000,
> Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> Hi Marc,
>>
>> I believe the intent of this patch is to protect the host/KVM against a guest
>> that is using BBML2. The host/KVM always assumes BBML0 and therefore doesn't do
>> any operations that are allowed by the arch to cause a conflict abort. Therefore
>> the host doesn't need to handle it. But a guest could be taking advantage of
>> BBML2 and therefore it's architiecturally possible for a conflict abort to be
>> raised to EL2. I think today that would take down the host?
>>
>> So really I think this could be considered a stand-alone KVM
>> hardening improvement?
> 
> I'm not disputing the need for a TLB Conflict abort handler. It will
> be a good addition once we agree on what needs to be done.

OK great, glad we are on the same page. I'll leave Miko to work through the details.

> 
>>> However, it doesn't seem to me that the host is equipped to deal with
>>> this sort of exception for itself. Shouldn't you start with that?
>>
>> If the host isn't doing any BBML2 operations it doesn't need to handle it, I
>> don't think? Obviously that changes later in the series and Miko is adding the
>> required handling to the host.
> 
> Yes, and that's what I overlooked yesterday, and I replied to that
> change this morning.
> 
> Thanks,
> 
> 	M.
>