linux-kernel - Re: [PATCH v2 19/35] Documentation/x86: Document the new attack vector controls

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Message-ID: <CA+i-1C2mJYwQYF9WrCjBTO0rfyNtDW=r8ZTpMwySrKSniVtXSg@mail.gmail.com>
Date: Wed, 13 Nov 2024 17:19:11 +0100
From: Brendan Jackman <jackmanb@...gle.com>
To: "Kaplan, David" <David.Kaplan@....com>
Cc: "Manwaring, Derek" <derekmn@...zon.com>, "bp@...en8.de" <bp@...en8.de>, 
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>, "hpa@...or.com" <hpa@...or.com>, 
	"jpoimboe@...nel.org" <jpoimboe@...nel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "mingo@...hat.com" <mingo@...hat.com>, 
	"pawan.kumar.gupta@...ux.intel.com" <pawan.kumar.gupta@...ux.intel.com>, 
	"peterz@...radead.org" <peterz@...radead.org>, "tglx@...utronix.de" <tglx@...utronix.de>, 
	"x86@...nel.org" <x86@...nel.org>, "mlipp@...zon.at" <mlipp@...zon.at>, 
	"canellac@...zon.at" <canellac@...zon.at>
Subject: Re: [PATCH v2 19/35] Documentation/x86: Document the new attack
 vector controls

On Wed, 13 Nov 2024 at 17:00, Kaplan, David <David.Kaplan@....com> wrote:
> I wonder what would happen if there was a mitigation that was required when switching to another guest, but not to the broader host address space.

This is already the case for the mitigations that "go the other way":
IBPB protects the incoming domain from the outgoing one, but L1D flush
protects the outgoing from the incoming. So when you exit to the
unrestricted address space it never makes sense to flush L1D (everyone
trusts the kernel) but e.g. guest->guest still needs one.

> that may not be covered by asi_exit.

That's right, these other mitigations are part of asi_enter.