Re: [Xen-devel] [PATCH RFC v2 00/12] xen/x86: use per-vcpu stacks for 64 bit pv domains

[Juergen Gross <jgross@xxxxxxxx>]

On 23/01/18 09:40, Jan Beulich wrote:
>>>> On 23.01.18 at 06:50, <jgross@xxxxxxxx> wrote:
>> On 22/01/18 17:51, Jan Beulich wrote:
>>> But isn't that model having the same synchronization issues upon
>>> guest L4 updates which Andrew was fighting with?
>>
>> I don't think so, as the number of shadows will always only be max. 1
>> with my approach.
> 
> How can I know that? The overview mail doesn't talk about the
> intended shadowing algorithm afaics, and none of the patches
> (judging by their titles) implements any part thereof. In

Right. That's the reason I'm telling you about it.

> particular I'd be curious to know whether what you say will
> hold also for guests not making use of the intended PV ABI
> extension.

Those guests will still be vulnerable to cross-vcpu accesses to Xen
stacks regarding Meltdown. Linux kernel is vulnerable the same way
regarding its own stacks, so there is no new vulnerability added
for Linux running as pv guests (I have to admit I don't know whether
the same applies to BSD).


Juergen


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