linux-kernel - Re: [PATCH] x86/bugs: Do not enable IBPB at firmware entry when IBPB is not available

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Date:   Thu, 28 Jul 2022 17:18:31 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dimitri John Ledkov <dimitri.ledkov@...onical.com>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/bugs: Do not enable IBPB at firmware entry when IBPB
 is not available

On Thu, Jul 28, 2022 at 03:33:35PM +0100, Dimitri John Ledkov wrote:
> Azure public cloud (so it is Azure custom hyper-v hypervisor) these
> instance types https://docs.microsoft.com/en-us/azure/virtual-machines/dav4-dasv4-series

Thank you both for the info.

Virt is an awful piece of sh*t when it goes and emulates all kinds of
imaginary CPUs. And AMD machine *without* an IBPB which is affected by
retbleed. Well, f*ck that.

Does that say somewhere on azure that those guests need to even enable
the mitigation or does the HV mitigate it for them?

Because I wouldn't mind to simply disable the mitigation when on a
hypervisor which doesn't support IBPB.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette