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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id r7sm19534725wmh.2.2020.12.21.10.12.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Dec 2020 10:12:34 -0800 (PST) Subject: Re: [PATCH] KVM: SVM: Add register operand to vmsave call in sev_es_vcpu_load To: Nathan Chancellor Cc: Tom Lendacky , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Nick Desaulniers , Sami Tolvanen References: <20201219063711.3526947-1-natechancellor@gmail.com> From: Paolo Bonzini Message-ID: Date: Mon, 21 Dec 2020 19:12:33 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201219063711.3526947-1-natechancellor@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/12/20 07:37, Nathan Chancellor wrote: > When using LLVM's integrated assembler (LLVM_IAS=1) while building > x86_64_defconfig + CONFIG_KVM=y + CONFIG_KVM_AMD=y, the following build > error occurs: > > $ make LLVM=1 LLVM_IAS=1 arch/x86/kvm/svm/sev.o > arch/x86/kvm/svm/sev.c:2004:15: error: too few operands for instruction > asm volatile(__ex("vmsave") : : "a" (__sme_page_pa(sd->save_area)) : "memory"); > ^ > arch/x86/kvm/svm/sev.c:28:17: note: expanded from macro '__ex' > #define __ex(x) __kvm_handle_fault_on_reboot(x) > ^ > ./arch/x86/include/asm/kvm_host.h:1646:10: note: expanded from macro '__kvm_handle_fault_on_reboot' > "666: \n\t" \ > ^ > :2:2: note: instantiated into assembly here > vmsave > ^ > 1 error generated. > > This happens because LLVM currently does not support calling vmsave > without the fixed register operand (%rax for 64-bit and %eax for > 32-bit). This will be fixed in LLVM 12 but the kernel currently supports > LLVM 10.0.1 and newer so this needs to be handled. > > Add the proper register using the _ASM_AX macro, which matches the > vmsave call in vmenter.S. > > Fixes: 861377730aa9 ("KVM: SVM: Provide support for SEV-ES vCPU loading") > Link: https://reviews.llvm.org/D93524 > Link: https://github.com/ClangBuiltLinux/linux/issues/1216 > Signed-off-by: Nathan Chancellor > --- > arch/x86/kvm/svm/sev.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > index e57847ff8bd2..958370758ed0 100644 > --- a/arch/x86/kvm/svm/sev.c > +++ b/arch/x86/kvm/svm/sev.c > @@ -2001,7 +2001,7 @@ void sev_es_vcpu_load(struct vcpu_svm *svm, int cpu) > * of which one step is to perform a VMLOAD. Since hardware does not > * perform a VMSAVE on VMRUN, the host savearea must be updated. > */ > - asm volatile(__ex("vmsave") : : "a" (__sme_page_pa(sd->save_area)) : "memory"); > + asm volatile(__ex("vmsave %%"_ASM_AX) : : "a" (__sme_page_pa(sd->save_area)) : "memory"); > > /* > * Certain MSRs are restored on VMEXIT, only save ones that aren't > Queued, thanks. Paolo