From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 25A6425FA10; Thu, 29 Jan 2026 15:58:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769702342; cv=none; b=qiCNgaqu0fQHA6h62H2lGnKpErp2RiaKbYXlYyz7cXipqUZddNgIIXe87BUmQ8loINq6yFjwG19piODMPRppFHPcSTKw0vu9CYXABxdb8zMrnWl4V/gA4R/b91NkE5gOcNEfqd+UBI6yGz+sBXHs+PqkDxLM5NC7XomJKv3kDtc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769702342; c=relaxed/simple; bh=c5eoXpc0WBa6sSJ4rHWXCWmWfiAREYl+zESFSrBFGnQ=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=B8Gc1Ls3+WFA4VzkrKP0J8GgfxPaWY1Ubj3uhRpu8cN+fsrlK0zFZoOJfLIGXaJ6ra7NdblLVD1d/JKx7r9QJNJN3u6kzWpn7O0e/KmgKh49Wu9hOJk79Gtnko9XRXyQd8QwPHO+0EABzA9BVCq9XVeHCMzAayc14UmL/gPcXe0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=cWUOlz9S; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="cWUOlz9S" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=c5eoXpc0WBa6sSJ4rHWXCWmWfiAREYl+zESFSrBFGnQ=; b=cWUOlz9SZZVwVXfmeWFL2WqWfV 6i5PDwSeRUCaXjT0FIeIOcRrJkMfu9XhOgBHF6S80emvIUSLJd5JWdq7Ifk7vUAl5b9qmxnmWMI/6 /s1nE9MWferlEC1+F5GdABvkEQPyfV7IobDiE574TTxXSQ2U4+O6K6xGAvSijgZPhoOgrcN2tbJUW hdyOBCIAxeUqY57me74YXMCKTl/XGBTVIofV5l/MOLIojG3/5jQfLat8geAApfLRnd58B5zkG3YdI zhdxSDQZoWJfvivMO8cySm9vUOb5pgxSQd633V2NIOfq1z7xnb5WYvC7lj2+NRG7gfAwufvGfqAWP AL0UtlzQ==; Received: from [2001:8b0:10b::4] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vlUPv-0000000Ac1g-07cF; Thu, 29 Jan 2026 15:58:47 +0000 Message-ID: Subject: Re: [PATCH v5 4/3] KVM: selftests: Add test cases for EOI suppression modes From: David Woodhouse To: Sean Christopherson Cc: Khushit Shah , pbonzini@redhat.com, kai.huang@intel.com, mingo@redhat.com, x86@kernel.org, bp@alien8.de, hpa@zytor.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, dave.hansen@linux.intel.com, tglx@linutronix.de, jon@nutanix.com, shaju.abraham@nutanix.com Date: Thu, 29 Jan 2026 07:58:41 -0800 In-Reply-To: References: <20251229111708.59402-1-khushit.shah@nutanix.com> <83f9b0a5dd0bc1de9d1e61954f6dd5211df45163.camel@infradead.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-6hWMlpTpwAoCDpDB7KjS" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-6hWMlpTpwAoCDpDB7KjS Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2026-01-29 at 07:19 -0800, Sean Christopherson wrote: > On Wed, Jan 28, 2026, David Woodhouse wrote: > > From: David Woodhouse > >=20 > > Rather than being frightened of doing the right thing for the in-kernel > > I/O APIC because "there might be bugs",=20 >=20 > I'm not worried about bugs per se, I'm worried about breaking existing gu= ests. > Even if KVM is 100% perfect, changes in behavior can still break guests, > especially for a feature like this where it seems like everyone got it wr= ong. There's the potential for guest bugs when the local APIC actually starts honouring the DIRECTED_EOI bit in the SPIV register, sure. At that point, the guest *has* to do the direct EOI (and it has to work). But that's why we kept the 'quirk' mode as the default unless userspace explicitly opts in. And it's true for the split-irqchip too; fixing the behaviour is the whole point of this exercise. I don't see why supporting precisely the same behaviour in the kernel irqchip is any different in that respect. > And as I said before, I'm not opposed to supporting directed EOI in the i= n-kernel > I/O APIC, but (a) I don't want to do it in conjunction with the fixes for= stable@, > and (b) I'd prefer to not bother unless there's an actual use case for do= ing so. > The in-kernel I/O APIC isn't being deprecated, but AFAIK it's being de-pr= ioritized > by pretty much every VMM.=C2=A0 I.e. the risk vs. reward isn't there for = me. I tend to favour the simplicity, with _ENABLE and _DISABLE just quietly doing what their name implies without any of that nonsense about "except if you have a kernel irqchip". But as you wish. Most of this test case should be fine on v6 of the patch which dropped in-kernel I/O APIC support. All the tests are conditional on the corresponding support being advertised, so it just needs updating to correctly detect the in-kernel _ENABLE support in case that does get added. 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