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[54.240.197.232]) by smtp.gmail.com with ESMTPSA id s18-20020adfecd2000000b002bdfcd8c77csm4507833wro.101.2023.01.16.08.36.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Jan 2023 08:36:33 -0800 (PST) From: Paul Durrant X-Google-Original-From: Paul Durrant Message-ID: Date: Mon, 16 Jan 2023 16:36:30 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH v6 12/51] i386/xen: Implement SCHEDOP_poll and SCHEDOP_yield Content-Language: en-US To: David Woodhouse , qemu-devel@nongnu.org Cc: Paolo Bonzini , Joao Martins , Ankur Arora , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Thomas Huth , =?UTF-8?Q?Alex_Benn=c3=a9e?= , Juan Quintela , "Dr . David Alan Gilbert" , Claudio Fontana , Julien Grall References: <20230110122042.1562155-1-dwmw2@infradead.org> <20230110122042.1562155-13-dwmw2@infradead.org> Organization: Xen Project In-Reply-To: <20230110122042.1562155-13-dwmw2@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::32d; envelope-from=xadimgnik@gmail.com; helo=mail-wm1-x32d.google.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 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, FREEMAIL_FROM=0.001, NICE_REPLY_A=-0.097, 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: , Reply-To: paul@xen.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 10/01/2023 12:20, David Woodhouse wrote: > From: David Woodhouse > > They both do the same thing and just call sched_yield. This is enough to > stop the Linux guest panicking when running on a host kernel which doesn't > intercept SCHEDOP_poll and lets it reach userspace. > > Signed-off-by: David Woodhouse Reviewed-by: Paul Durrant ... with some observations... > --- > target/i386/kvm/xen-emu.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c > index 5f2b55ef10..80005ea527 100644 > --- a/target/i386/kvm/xen-emu.c > +++ b/target/i386/kvm/xen-emu.c > @@ -227,6 +227,18 @@ static bool kvm_xen_hcall_sched_op(struct kvm_xen_exit *exit, X86CPU *cpu, > err = schedop_shutdown(cs, arg); > break; > > + case SCHEDOP_poll: > + /* > + * Linux will panic if this doesn't work. Just yield; it's not > + * worth overthinking it because wWith event channel handling Typo 'wWith'. Also possibly worth mentioning that the reason a yield is ok is because the semantics of the hypercall allow for spurious wake-up. > + * in KVM, the kernel will intercept this and it will never > + * reach QEMU anyway. > + */ > + case SCHEDOP_yield: > + sched_yield(); > + err = 0; > + break; > + > default: > return false; > }