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[92.26.107.252]) by smtp.gmail.com with ESMTPSA id o15-20020adfcf0f000000b00327de0173f6sm11432651wrj.115.2023.10.25.00.52.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 25 Oct 2023 00:52:51 -0700 (PDT) Message-ID: <654468cf-1563-4c1c-8c7c-076bc6dfbabf@citrix.com> Date: Wed, 25 Oct 2023 08:52:50 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Andrew Cooper Subject: Re: [RESEND][PATCH 1/6] x86/bugs: Add asm helpers for executing VERW Content-Language: en-GB To: Peter Zijlstra , Pawan Gupta Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Josh Poimboeuf , Andy Lutomirski , Jonathan Corbet , Sean Christopherson , Paolo Bonzini , tony.luck@intel.com, ak@linux.intel.com, tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, Alyssa Milburn , Daniel Sneddon , antonio.gomez.iglesias@linux.intel.com, Alyssa Milburn References: <20231020-delay-verw-v1-0-cff54096326d@linux.intel.com> <20231020-delay-verw-v1-1-cff54096326d@linux.intel.com> <20231025062818.7kaerqklaut7dg5r@desk> <20231025072255.GA37471@noisy.programming.kicks-ass.net> Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: <20231025072255.GA37471@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 25/10/2023 8:22 am, Peter Zijlstra wrote: > On Tue, Oct 24, 2023 at 11:28:18PM -0700, Pawan Gupta wrote: > >> With .text.entry section I am getting getting below warnings and an >> error: >> >> ----------------------------------------------------------------- >> LD vmlinux.o >> vmlinux.o: warning: objtool: .text.entry+0x0: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x40: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x80: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0xc0: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x100: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x140: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x180: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x1c0: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x200: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x240: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x280: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x2c0: unreachable instruction >> vmlinux.o: warning: objtool: .text.entry+0x300: unreachable instruction >> vmlinux.o: warning: objtool: .altinstr_replacement+0x2c: relocation to !ENDBR: .text.entry+0x0 >> vmlinux.o: warning: objtool: .altinstr_replacement+0x1c4: relocation to !ENDBR: .text.entry+0x0 >> vmlinux.o: warning: objtool: .altinstr_replacement+0x1d0: relocation to !ENDBR: .text.entry+0x0 >> vmlinux.o: warning: objtool: .altinstr_replacement+0x2d2: relocation to !ENDBR: .text.entry+0x80 >> vmlinux.o: warning: objtool: .altinstr_replacement+0x5d5: relocation to !ENDBR: .text.entry+0xc0 >> OBJCOPY modules.builtin.modinfo >> GEN modules.builtin >> MODPOST vmlinux.symvers >> UPD include/generated/utsversion.h >> CC init/version-timestamp.o >> LD .tmp_vmlinux.kallsyms1 >> ld: error: unplaced orphan section `.text.entry' from `vmlinux.o' >> make[2]: *** [scripts/Makefile.vmlinux:36: vmlinux] Error 1 >> ----------------------------------------------------------------- >> >> ... because my config has CONFIG_LD_ORPHAN_WARN_LEVEL="error" and >> objtool needs to be told about this entry. >> >> Do you think its worth fighting these warnings and error, or simply use >> .rodata section for verw memory operand? > I'm thinking you need to at the very least stay in a section that's > actually still mapped with PTI :-) Sorry.  Xen and Linux have this section named opposite ways around. > diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S > index bfb7bcb362bc..9eb2b532c92a 100644 > --- a/arch/x86/entry/entry.S > +++ b/arch/x86/entry/entry.S > @@ -20,3 +22,16 @@ SYM_FUNC_END(entry_ibpb) > EXPORT_SYMBOL_GPL(entry_ibpb); > > .popsection > + > +.pushsection .entry.text, "ax" > + > +.align 64 > +SYM_CODE_START_NOALIGN(mds_verw_sel) > + UNWIND_HINT_UNDEFINED > + ANNOTATE_NOENDBR > +1: > + .word __KERNEL_DS > + .skip 64 - (. - 1b), 0xcc The 1 label aliases mds_verw_sel and this must remain like this for the construct to work. So instead of .skip, why not simply .align 64, 0xcc and get rid of the 1: label? Do we have a suitably named constant cacheline size, rather than opencoding 64? > +SYM_CODE_END(mds_verw_sel); Given that KVM needs it, this probably needs an EXPORT_SYMBOL_GPL() on it. ~Andrew