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[31.30.173.16]) by smtp.gmail.com with ESMTPSA id h17-20020a1709070b1100b00a558206b2c5sm8516279ejl.99.2024.04.25.08.58.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Apr 2024 08:58:16 -0700 (PDT) Date: Thu, 25 Apr 2024 17:58:15 +0200 From: Andrew Jones To: Daniel Henrique Barboza Cc: qemu-devel@nongnu.org, qemu-riscv@nongnu.org, alistair.francis@wdc.com, bmeng@tinylab.org, liwei1518@gmail.com, zhiwei_liu@linux.alibaba.com, palmer@rivosinc.com Subject: Re: [PATCH v2 1/1] target/riscv/kvm: tolerate KVM disable ext errors Message-ID: <20240425-92aa48159348b26bbae5edbc@orel> References: <20240422171425.333037-1-dbarboza@ventanamicro.com> <20240422171425.333037-2-dbarboza@ventanamicro.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240422171425.333037-2-dbarboza@ventanamicro.com> Received-SPF: pass client-ip=2a00:1450:4864:20::533; envelope-from=ajones@ventanamicro.com; helo=mail-ed1-x533.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Mon, Apr 22, 2024 at 02:14:25PM GMT, Daniel Henrique Barboza wrote: > Running a KVM guest using a 6.9-rc3 kernel, in a 6.8 host that has zkr > enabled, will fail with a kernel oops SIGILL right at the start. The > reason is that we can't expose zkr without implementing the SEED CSR. > Disabling zkr in the guest would be a workaround, but if the KVM doesn't > allow it we'll error out and never boot. > > In hindsight this is too strict. If we keep proceeding, despite not > disabling the extension in the KVM vcpu, we'll not add the extension in > the riscv,isa. The guest kernel will be unaware of the extension, i.e. > it doesn't matter if the KVM vcpu has it enabled underneath or not. So > it's ok to keep booting in this case. > > Change our current logic to not error out if we fail to disable an > extension in kvm_set_one_reg(), but show a warning and keep booting. It > is important to throw a warning because we must make the user aware that > the extension is still available in the vcpu, meaning that an > ill-behaved guest can ignore the riscv,isa settings and use the > extension. > > The case we're handling happens with an EINVAL error code. If we fail to > disable the extension in KVM for any other reason, error out. > > We'll also keep erroring out when we fail to enable an extension in KVM, > since adding the extension in riscv,isa at this point will cause a guest > malfunction because the extension isn't enabled in the vcpu. > > Suggested-by: Andrew Jones > Signed-off-by: Daniel Henrique Barboza > --- > target/riscv/kvm/kvm-cpu.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c > index 6a6c6cae80..03e3fee607 100644 > --- a/target/riscv/kvm/kvm-cpu.c > +++ b/target/riscv/kvm/kvm-cpu.c > @@ -427,10 +427,14 @@ static void kvm_riscv_update_cpu_cfg_isa_ext(RISCVCPU *cpu, CPUState *cs) > reg = kvm_cpu_cfg_get(cpu, multi_ext_cfg); > ret = kvm_set_one_reg(cs, id, ®); > if (ret != 0) { > - error_report("Unable to %s extension %s in KVM, error %d", > - reg ? "enable" : "disable", > - multi_ext_cfg->name, ret); > - exit(EXIT_FAILURE); > + if (!reg && ret == -EINVAL) { > + warn_report("KVM cannot disable extension %s", > + multi_ext_cfg->name); > + } else { > + error_report("Unable to enable extension %s in KVM, error %d", > + multi_ext_cfg->name, ret); > + exit(EXIT_FAILURE); > + } > } > } > } > -- > 2.44.0 > Reviewed-by: Andrew Jones