From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 398D44963B7; Tue, 19 May 2026 12:56:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779195389; cv=none; b=jcQjqgYAJx26x/lmRwjGlvMAhjE4RC1pZ7Ch4Duro9WYeGyAQggviFrFaMwF0W2dTOE9DXDda+Y5GFh72Q11A0S6ZmhgIZPdCgKikvTZba2fFMXO5rksPEgWCTTy/Vxfz1JrrraXb8hiw3bnmig+efYdbdQ69fp65j0n5YOSe1U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779195389; c=relaxed/simple; bh=swiLRF5viUP9Bya8Dp7YZueJwlHQOjHir4JEE0vhuWA=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=q/eYVtjiLgbMt6txJFVi8RPy5Wyas4AgD84f7v3LuvTzCueTvOLdpXyiregpIN+0iW4h8w0JC4BpNpnWgnMC8NNGhg48K9MrIuRvTulzlOLbcjwXZvMl0z1CW63MuGumrhYBKMojy6KP4Pd4uCr/22bXwby9PKQwQKQ7qCq97CU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=onCKr4Fe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="onCKr4Fe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C78B7C2BCB3; Tue, 19 May 2026 12:56:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1779195388; bh=swiLRF5viUP9Bya8Dp7YZueJwlHQOjHir4JEE0vhuWA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=onCKr4FekH7xM2LVd2O8ZpVN+C9BcX2DiYfqmoUuV4SMKcB+Q1w11YKXTHrUZzkIV G3VAnCJ+nvfKPMdQGwyaV2ryg4bSurZAHT87CiQKtHPANc7qEm9IkWYNBWJMSQ7j3u lM5FVi+MS0LYxjAE7hInPG7JUzwqRJIfiMEY/hsBxjEQD92QaoaVT6NZGzPpWCKcHJ xOknyTHnF6tvmlPfhwPC0y1g4U8VyK7hbACcjCriLoJQRIY5AnY5XCdJ+QT3hPRJpV Bg8PNLF7W7YiSYMqEbb0TrBTd7lX2t6p03dei5jlv/GTOY4cnif6wb/VbHFtMhgJRc 7mTGJdsH1PoOQ== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.98.2) (envelope-from ) id 1wPJzm-00000003xSA-1yzQ; Tue, 19 May 2026 12:56:26 +0000 Date: Tue, 19 May 2026 13:56:26 +0100 Message-ID: <86pl2rwoat.wl-maz@kernel.org> From: Marc Zyngier To: Paolo Bonzini Cc: David Woodhouse , Will Deacon , Jonathan Corbet , Shuah Khan , kvm , Linux Doc Mailing List , "Kernel Mailing List, Linux" , Sean Christopherson , Jim Mattson , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Raghavendra Rao Ananta , Eric Auger , Kees Cook , Arnd Bergmann , Nathan Chancellor , linux-arm-kernel , kvmarm@lists.linux.dev, linux-kselftest Subject: Re: [PATCH] Documentation: KVM: Document guest-visible compatibility expectations In-Reply-To: <86qzn7wp3y.wl-maz@kernel.org> References: <6856b269d2af706eae397e0cf9c1231f89d9a932.camel@infradead.org> <6afc4b95-3c15-4d71-877d-19b84e91ce05@redhat.com> <57bc082f4824d6114d3156744c25986effc29aca.camel@infradead.org> <86h5obya2r.wl-maz@kernel.org> <48b06e5655d56ff6eda30e563b34894fa0eb2f07.camel@infradead.org> <3f9d731c3d26b0367600f1069e6425099bc34eac.camel@infradead.org> <86qzn7wp3y.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/30.1 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: pbonzini@redhat.com, dwmw2@infradead.org, will@kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, seanjc@google.com, jmattson@google.com, oupton@kernel.org, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, rananta@google.com, eric.auger@redhat.com, kees@kernel.org, arnd@arndb.de, nathan@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kselftest@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false On Tue, 19 May 2026 13:38:57 +0100, Marc Zyngier wrote: > > As I said before, I'd be OK with something that would restore IIDR to > REV1. But not something that actively breaks the GIC emulation by > reintroducing a bug. That's, by construction, dead code that will only > bitrot, because there is no SW that can make use of this nonsense. I will also add that if we make it a policy to preserve buggy behaviours that the guest cannot be relying on, then I question whether we should be fixing anything at all. For example, 6.19 fixed a totally buggy behaviour where a guest couldn't not have more than (on most HW) 4 interrupts in flight at any given time. This was obviously totally bogus, and this was fixed unconditionally, as legitimate guests could experience gold-platted lock-ups. Should we revert to the previous behaviour? In the affirmative, I will simply stop fixing things, and someone else can have fun retrofitting buggy crap. M. -- Without deviation from the norm, progress is not possible.