From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2309B4F3906; Mon, 28 Sep 2026 17:05:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790615112; cv=none; b=pPSzFoKVQs7dHaIhb7O3IagmBbETuC5+th+ppjkkd3GufOkdeiU9BWhzXfKB0JsikVLmn1ddtmcLb2d5H5lAsVFSmdBLal5j0jbZMK5O2AJ06WkC5MCBrQdF+3ktBYZj3Jx+Pw8B8I33zaEKu00ZgGHplBcEU6qlVkfhWEWthXI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790615112; c=relaxed/simple; bh=yoXTXqPzTE35yeLLUFkb8ceBe47d/S/Yap+eGL4p4bI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=DvZ5n4Tcil9kS9iOUBruFDIuLFLHr4PuyaHYWJdMShiDoaJqsAOgJ1l4bkLGQqDqfYu11Sjz+7DpmJBBYVxsBSYCAU66cahXj2Z08zBwP+9OOqu5Qxe4svjBp4abHuBoPZ1kg66wy2Zh56R12JgHlXt1t62W5A9rK1IrcfLBlKI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QdQwx718; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QdQwx718" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C955C1F00893; Mon, 28 Sep 2026 17:05:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790615111; bh=yoXTXqPzTE35yeLLUFkb8ceBe47d/S/Yap+eGL4p4bI=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=QdQwx718ik84L+Mq45KEayXLdVMUAcnmUhtWIQfGQXGH9vNemnBJYzTv7sICCtRE+ 39+4B+n3qedPT1V8sl+2ygYB09kLPI75LxEkCv+ptk3g6uZl3mI84+2geK26zblJVE dU3VPa+mYT9RQGE2FWVdw4TEfsCGJJTAjLV9ro+gbqN5ctgqWbX0iNcdk7KDcxbZTS 9OSzG3RytUq0zqCEU4v7C/uqLpG35ZMCaMpPw3ZhQXrShg9Xi0z7w/ReikxlR0bMJF +xQJVbH2q5IZtgeGlH69O9wfIiwUTppVz0/Msyj/Uyt34iWlg7pBcpkIunSyMvzIR/ 2wBtg1LjB0MIA== Date: Mon, 28 Sep 2026 10:05:09 -0700 From: Oliver Upton To: Fuad Tabba Cc: Marc Zyngier , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Joey Gouly , Suzuki K Poulose , Zenghui Yu , Steffen Eiden , Catalin Marinas , Will Deacon , Mark Rutland , Quentin Perret , Vincent Donnefort , Wei-Lin Chang , Fuad Tabba , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/4] KVM: arm64: Don't WARN on an unsupported TLBI OS from vEL1 Message-ID: References: <20260928064643.3265087-1-fuad.tabba@linux.dev> <20260928064643.3265087-2-fuad.tabba@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260928064643.3265087-2-fuad.tabba@linux.dev> Hi Fuad, On Mon, Sep 28, 2026 at 07:46:40AM +0100, Fuad Tabba wrote: > KVM hides TLBI OS from a guest whose ID registers don't advertise it by > trapping the instructions: through the fine-grained traps on a CPU with > FGT, and through HCR_EL2.TTLBOS on one with FEAT_EVT2. With FGT, > triage_sysreg_trap() makes a trapped TLBI OS UNDEFINED. Without it, the > instruction reaches handle_tlbi_el1(), which assumes an EL1 TLBI only > traps from a guest at vEL2 and WARNs before checking whether the guest > supports it. The guest still gets its UNDEF after the WARN. A VMM can > trigger the WARN by hiding TLBI OS and having the guest execute one. So the FGUs don't actually require any hardware support, they're just a representation of our UNDEF emulation that can be applied even on non-FGT. That's actually the way we had them wired before the whole config.c rewrite. Can you look into reinstating the FGUs? Thanks, Oliver