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Wed, 07 Jun 2023 12:47:23 -0700 (PDT) Date: Wed, 7 Jun 2023 12:47:21 -0700 From: Isaku Yamahata To: Dave Hansen Cc: Isaku Yamahata , Kai Huang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, kirill.shutemov@linux.intel.com, tony.luck@intel.com, peterz@infradead.org, tglx@linutronix.de, seanjc@google.com, pbonzini@redhat.com, david@redhat.com, dan.j.williams@intel.com, rafael.j.wysocki@intel.com, ying.huang@intel.com, reinette.chatre@intel.com, len.brown@intel.com, ak@linux.intel.com, isaku.yamahata@intel.com, chao.gao@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, bagasdotme@gmail.com, sagis@google.com, imammedo@redhat.com Subject: Re: [PATCH v11 05/20] x86/virt/tdx: Add SEAMCALL infrastructure Message-ID: <20230607194721.GI2244082@ls.amr.corp.intel.com> References: <92e19d74-447f-19e0-d9ec-8a3f12f04927@intel.com> <20230607185355.GH2244082@ls.amr.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1CD18120013 X-Stat-Signature: x35wxsjxd86nrzghmrzqw9htsrg67bof X-HE-Tag: 1686167244-306847 X-HE-Meta: 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 qdMLL4UE 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 07, 2023 at 12:27:33PM -0700, Dave Hansen wrote: > On 6/7/23 11:53, Isaku Yamahata wrote: > >>> VMX enabling, and KVM is the only user of TDX. This implementation > >>> chooses to make KVM itself responsible for enabling VMX before using > >>> TDX and let the rest of the kernel stay blissfully unaware of VMX. > >>> > >>> The current TDX_MODULE_CALL macro handles neither #GP nor #UD. The > >>> kernel would hit Oops if SEAMCALL were mistakenly made w/o enabling VMX > >>> first. Architecturally, there is no CPU flag to check whether the CPU > >>> is in VMX operation. Also, if a BIOS were buggy, it could still report > >>> valid TDX private KeyIDs when TDX actually couldn't be enabled. > >> I'm not sure this is a great justification. If the BIOS is lying to the > >> OS, we _should_ oops. > >> > >> How else can this happen other than silly kernel bugs. It's OK to oops > >> in the face of silly kernel bugs. > > TDX KVM + reboot can hit #UD. On reboot, VMX is disabled (VMXOFF) via > > syscore.shutdown callback. However, guest TD can be still running to issue > > SEAMCALL resulting in #UD. > > > > Or we can postpone the change and make the TDX KVM patch series carry a patch > > for it. > > How does the existing KVM use of VMLAUNCH/VMRESUME avoid that problem? extable. From arch/x86/kvm/vmx/vmenter.S .Lvmresume: vmresume jmp .Lvmfail .Lvmlaunch: vmlaunch jmp .Lvmfail _ASM_EXTABLE(.Lvmresume, .Lfixup) _ASM_EXTABLE(.Lvmlaunch, .Lfixup) -- Isaku Yamahata