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[35.205.13.209]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48710fd2c4esm38080035e9.4.2026.03.24.08.04.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Mar 2026 08:04:33 -0700 (PDT) Date: Tue, 24 Mar 2026 15:04:29 +0000 From: Sebastian Ene To: Marc Zyngier Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, android-kvm@google.com, catalin.marinas@arm.com, joey.gouly@arm.com, mark.rutland@arm.com, oupton@kernel.org, suzuki.poulose@arm.com, tabba@google.com, vdonnefort@google.com, will@kernel.org, yuzenghui@huawei.com Subject: Re: [PATCH] KVM: arm64: Inject UNDEF when host is executing an smc with imm16 != 0 Message-ID: References: <20260324135728.3532400-1-sebastianene@google.com> <86tsu547ao.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86tsu547ao.wl-maz@kernel.org> On Tue, Mar 24, 2026 at 02:43:27PM +0000, Marc Zyngier wrote: > On Tue, 24 Mar 2026 13:57:28 +0000, > Sebastian Ene wrote: > > > > The ARM Service Calling Convention (SMCCC) specifies that the function > > identifier and parameters should be passed in registers, leaving the > > 16-bit immediate field of the SMC instruction un-handled. > > Currently, our pKVM handler ignores the immediate value, which could lead > > to non-compliant software relying on implementation-defined behavior. > > Enforce the host kernel running under pKVM to use an immediate value > > of 0 by decoding the ISS from the ESR_EL2 and inject an undefined > > instruction exception back to the caller. Hi Marc, > > No, that's completely wrong. SMC never UNDEFs, unless EL3 isn't > implemented. You can't just decide to generate an UNDEF because you > don't like the immediate. > > All you are allowed to do is to return an error code. Thanks for letting me know, I will update the patch to do this. > > Thanks, > > M. > Cheers, Sebastian > -- > Without deviation from the norm, progress is not possible.