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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) 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260519_055629_832383_5023DA4D X-CRM114-Status: GOOD ( 16.25 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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.