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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id y3sm2801269pjg.7.2021.09.21.06.50.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Sep 2021 06:50:13 -0700 (PDT) Date: Tue, 21 Sep 2021 13:50:09 +0000 From: Sean Christopherson To: Ashish Kalra Cc: Steve Rutherford , pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, joro@8bytes.org, bp@alien8.de, thomas.lendacky@amd.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, brijesh.singh@amd.com, dovmurik@linux.ibm.com, tobin@linux.ibm.com, jejb@linux.ibm.com, dgilbert@redhat.com Subject: Re: [PATCH v6 1/5] x86/kvm: Add AMD SEV specific Hypercall3 Message-ID: References: <6fd25c749205dd0b1eb492c60d41b124760cc6ae.1629726117.git.ashish.kalra@amd.com> <20210921095838.GA17357@ashkalra_ubuntu_server> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210921095838.GA17357@ashkalra_ubuntu_server> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 21, 2021, Ashish Kalra wrote: > This is simply a Hack, i don't think this is a good approach to take forward. But a clever hack ;-) > > Unless there's some fundamental technical hurdle I'm overlooking, if pv_ops can > > be configured early enough to handle this, then so can alternatives. > > Now, as i mentioned earlier, apply_alternatives() is only called boot > CPU identification has been done which is a lot of support code which > may be dependent on earlier setup_arch() code and then it does CPU > mitigtion selections before patching alternatives, again which may have > dependencies on previous code paths in setup_arch(), so i am not sure if > we can call apply_alternatives() earlier. apply_alternatives() is a generic helper that can work on any struct alt_instr array, e.g. KVM_HYPERCALL can put its alternative into a different section that's patched as soon as the VMM is identified. > Maybe for a guest kernel and virtualized boot enviroment, CPU > identification may not be as complicated as for a physical host, but > still it may have dependencies on earlier architecture specific boot > code. > > > Adding notify_page_enc_status_changed() may be necessary in the future, e.g. for TDX > > or SNP, but IMO that is orthogonal to adding a generic, 100% redundant helper. > > If we have to do this in the future and as Sean mentioned ealier that > vmcall needs to be fixed for TDX (as it will cause a #VE), then why not > add this abstraction right now ? I'm not objecting to adding a PV op, I'm objecting to kvm_sev_hypercall3(). If others disagree and feel it's the way forward, I certainly won't stand in the way, but IMO it's unnecessary code duplication.