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([2001:b07:6468:f312:ec9b:111a:97e3:4baf]) by smtp.gmail.com with ESMTPSA id 97sm3895548wrm.15.2020.09.25.13.40.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Sep 2020 13:40:35 -0700 (PDT) Subject: Re: [PATCH v1 1/3] i386: Remove the limitation of IP payloads for Intel PT To: Eduardo Habkost References: <1582580312-19864-1-git-send-email-luwei.kang@intel.com> <1582580312-19864-2-git-send-email-luwei.kang@intel.com> <20200925161539.GS3717385@habkost.net> <20200925165415.GT3717385@habkost.net> <036ba624-670c-d6b7-721c-ad5c9d648c1f@redhat.com> <20200925202956.GV3717385@habkost.net> From: Paolo Bonzini Message-ID: Date: Fri, 25 Sep 2020 22:40:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200925202956.GV3717385@habkost.net> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=pbonzini@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/25 01:07:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.199, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.238, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "qemu-devel@nongnu.org" , "Kang, Luwei" , "Strong, Beeman" , "rth@twiddle.net" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 25/09/20 22:29, Eduardo Habkost wrote: >> No, it's not possible. KVM doesn't have a say on what the processor >> writes in the tracing packets. > Can KVM refuse to enable packet generation if CSbase is not zero > and CPUID.(EAX=14H,ECX=0)[bit 31] seen by guest is different from > host? Yes, but the processor could change operating mode (and hence CSbase) while tracing is active. This is very unlikely, since it would require nonzero CS-base and a 32-bit host, but in principle not impossible (could be a firmware call, for example). The only solution is for KVM to accept both, and for QEMU to refuse a setting that does not match the host. Paolo