From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Gibson Date: Fri, 03 Sep 2021 05:13:55 +0000 Subject: Re: [PATCH 0/5] KVM: PPC: Book3S: Modules cleanup and unification Message-Id: MIME-Version: 1 Content-Type: multipart/mixed; boundary="ZzHFj0RmvuubG6he" List-Id: References: <20210901173357.3183658-1-farosas@linux.ibm.com> <875yvjujxy.fsf@linux.ibm.com> In-Reply-To: <875yvjujxy.fsf@linux.ibm.com> To: Fabiano Rosas Cc: linuxppc-dev@lists.ozlabs.org, npiggin@gmail.com, kvm-ppc@vger.kernel.org --ZzHFj0RmvuubG6he Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Sep 02, 2021 at 11:32:41AM -0300, Fabiano Rosas wrote: > David Gibson writes: >=20 > > On Wed, Sep 01, 2021 at 02:33:52PM -0300, Fabiano Rosas wrote: > >> This series merges our three kvm modules kvm.ko, kvm-hv.ko and > >> kvm-pr.ko into one kvm.ko module. > > > > That doesn't sound like a good idea to me. People who aren't on BookS > > servers don't want - and can't use - kvm-hv. Almost nobody wants > > kvm-pr. It's also kind of inconsistent with x86, which has the > > separate AMD and Intel modules. >=20 > But this is not altering the ability of having only kvm-hv or only > kvm-pr. I'm taking the Kconfig options that used to produce separate > modules and using them to select which code gets built into the one > kvm.ko module. >=20 > Currently: >=20 > CONFIG_KVM_BOOK3S_64=3Dm <-- produces kvm.ko > CONFIG_KVM_BOOK3S_64_HV=3Dm <-- produces kvm-hv.ko > CONFIG_KVM_BOOK3S_64_PR=3Dm <-- produces kvm-pr.ko >=20 > I'm making it so we now have one kvm.ko everywhere, but there is still: >=20 > CONFIG_KVM_BOOK3S_64=3Dm <-- produces kvm.ko > CONFIG_KVM_BOOK3S_HV_POSSIBLE=3Dy <-- includes HV in kvm.ko > CONFIG_KVM_BOOK3S_PR_POSSIBLE=3Dy <-- includes PR in kvm.ko >=20 > In other words, if you are going to have at least two modules loaded at > all times (kvm + kvm-hv or kvm + kvm-pr), why not put all that into one > module? No one needs to build code they are not going to use, this is > not changing. Ah.. I see, you're removing the runtime switch from one to the other at the same time as having just a single one loaded, but leaving the ability to compile time switch. And compile time is arguably good enough for the cases I've described. Ok, I see your point. I still think it's conceptually not ideal, but the practical benefit is more important. Objection withdrawn. > About consistency with x86, this situation is not analogous because we > need to be able to load both modules at the same time, which means > kvm.ko needs to stick around when one module goes away in case we want > to load the other module. The KVM common code states that it expects to > have at most one implementation: >=20 > /* > * kvm_arch_init makes sure there's at most one caller > * for architectures that support multiple implementations, > * like intel and amd on x86. > (...) >=20 > which is not true in our case due to this requirement of having two > separate modules loading independently. >=20 > (tangent) We are already quite different from other architectures since > we're not making use of kvm_arch_init and some other KVM hooks, such as > kvm_arch_check_processor_compat. So while other archs have their init > dispatched by kvm common code, our init and cleanup happens > independently in the ppc-specific modules, which obviously works but is > needlessly different and has subtleties in the ordering of operations > wrt. the kvm common code. (tangent) >=20 --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --ZzHFj0RmvuubG6he Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEdfRlhq5hpmzETofcbDjKyiDZs5IFAmExrxMACgkQbDjKyiDZ s5KohA/9Gfq6pHibFuBWjrN/3iQF/0n0TzlL6x1jWavUn8C6eW+QySpkHDQ1CMV0 27NLIaan0NNq7H4TDxeI4QnVlJOQUXxeTKmtbi8F3fdTceF61M4frRMtH5sMS5fC 0g+t5vzD4Hd1cz8d/fuVVGWiR8HI+L6+ft+V2F7qQA1ruHcG1TPhMFKg+iZidfnL JEfQHgyQseyYxux96pMumgXHWnX5N5jvvcjMKl22PWQaQRGuavt+iqNeeUTFFrCD q7VTBsJwvmaXZ255MrbMT7DDtNMFEy/PbV5tWbM7Lb6Y5IQvDeK+kwUsZKi1cYph U8RzVueTpF2yeK58ZyypXNB8EgMK6SiSycy/Wc1eyiPE4MCFmw0eVgjW4AdUtZpv 4/H8u4+izQOBOLZZ1MoXU36Tdap8v1ApPnFiMTRycIrbEBKJURzjakrI+IDerJF5 6fvfTP1/60PUhdNkjSBDa6SoLi3AKAhetiNcIwAoo4jhIykwoRe+QLTg+ZAzQi2X SXAKwMKlF8AacTfilP5qiZ0P00UO7fDyDwHXJ5IrPeHNwb+38MbA33d+K9eOgqCv LtNw6HuGK7G9Z6RPWEB0hrhEPVjeqw3XPLxxkXesEHOnnA+nBMC/gcoiEGCkTF2s Hw7nJGIsPDYug//XJxY9LQkIV82qkkM9t407sEEoQC2Q+XEstpQ= =hJiE -----END PGP SIGNATURE----- --ZzHFj0RmvuubG6he--