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Tue, 17 Jun 2025 10:17:13 -0400 (EDT) Received: by mbp.qyliss.net (Postfix, from userid 1000) id BC3469A0A3C; Tue, 17 Jun 2025 16:17:11 +0200 (CEST) From: Alyssa Ross To: Eric Auger , eric.auger.pro@gmail.com, eric.auger@redhat.com, qemu-devel@nongnu.org, qemu-arm@nongnu.org, miguel.luis@oracle.com, peter.maydell@linaro.org, richard.henderson@linaro.org, maz@kernel.org, gkulkarni@amperecomputing.com, gankulkarni@os.amperecomputing.com Subject: Re: [PATCH v5 5/5] hw/arm/virt: Allow virt extensions with KVM In-Reply-To: <20250527062534.1186004-6-eric.auger@redhat.com> References: <20250527062534.1186004-1-eric.auger@redhat.com> <20250527062534.1186004-6-eric.auger@redhat.com> Date: Tue, 17 Jun 2025 16:17:10 +0200 Message-ID: <875xgutpuh.fsf@alyssa.is> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha512; protocol="application/pgp-signature" Received-SPF: pass client-ip=202.12.124.141; envelope-from=hi@alyssa.is; helo=flow-b6-smtp.messagingengine.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-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+alex.bennee=linaro.org@nongnu.org Sender: qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org X-TUID: lTuyqp25x2Mj --=-=-= Content-Type: text/plain Eric Auger writes: > From: Haibo Xu > > Up to now virt support on guest has been only supported with TCG. > Now it becomes feasible to use it with KVM acceleration. > > Also check only in-kernel GICv3 is used along with KVM EL2. > > Signed-off-by: Haibo Xu > Signed-off-by: Miguel Luis > Signed-off-by: Eric Auger > Reviewed-by: Richard Henderson Hi! From what I can tell, this will produce an error on hosts that don't support nested virtualization when QEMU is invoked with -accel kvm:tcg -machine virtualization=on, but I don't think that's the ideal behaviour. It would make more sense for it to fall back to the first permitted accel option that does support running the machine as configured, so if hardware nested virtualization is not supported, it should fall back to TCG. I maintain an OS development environment that includes scripts for running images in QEMU, where running KVM on those images is a requirement. Currently, those scripts simply force TCG on aarch64. With this change, to take advantage of KVM NV support, I'd have to try to identify in the script whether NV would be supported. QEMU would be in a much better position to determine this and fall back to TCG if it's unsupported, like how the -accel option with multiple values usually works. --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEARYKAB0WIQRV/neXydHjZma5XLJbRZGEIw/wogUCaFF45gAKCRBbRZGEIw/w ok1AAP9QNkNFkNaw759IJnKaFhV3vMLiygMqSLbpUJkI0ubCOwEAm2MNXUbMBfet VqLAlJOhXL1IH8VLug590GWzT3HJaAo= =5p9U -----END PGP SIGNATURE----- --=-=-=--