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Mon, 14 Apr 2025 07:06:43 -0700 (PDT) Received: from [192.168.1.100] ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-acaa1ccd1cfsm916454566b.138.2025.04.14.07.06.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 14 Apr 2025 07:06:42 -0700 (PDT) Message-ID: <01c65464-8535-28d8-a9b5-eb4f90114e2d@gmail.com> Date: Mon, 14 Apr 2025 16:06:41 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [PATCH 4/6] x86,hyperv: Clean up hv_do_hypercall() To: Peter Zijlstra , x86@kernel.org Cc: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, jpoimboe@kernel.org, pawan.kumar.gupta@linux.intel.com, seanjc@google.com, pbonzini@redhat.com, ardb@kernel.org, kees@kernel.org, Arnd Bergmann , gregkh@linuxfoundation.org, linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-efi@vger.kernel.org, samitolvanen@google.com, ojeda@kernel.org References: <20250414111140.586315004@infradead.org> <20250414113754.285564821@infradead.org> Content-Language: en-US From: Uros Bizjak In-Reply-To: <20250414113754.285564821@infradead.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 14. 04. 25 13:11, Peter Zijlstra wrote: > What used to be a simple few instructions has turned into a giant mess > (for x86_64). Not only does it use static_branch wrong, it mixes it > with dynamic branches for no apparent reason. > > Notably it uses static_branch through an out-of-line function call, > which completely defeats the purpose, since instead of a simple > JMP/NOP site, you get a CALL+RET+TEST+Jcc sequence in return, which is > absolutely idiotic. > > Add to that a dynamic test of hyperv_paravisor_present, something > which is set once and never changed. > > Replace all this idiocy with a single direct function call to the > right hypercall variant. > > Signed-off-by: Peter Zijlstra (Intel) > --- > arch/x86/hyperv/hv_init.c | 21 ++++++ > arch/x86/hyperv/ivm.c | 14 ++++ > arch/x86/include/asm/mshyperv.h | 137 +++++++++++----------------------------- > arch/x86/kernel/cpu/mshyperv.c | 18 +++-- > 4 files changed, 88 insertions(+), 102 deletions(-) > > --- a/arch/x86/hyperv/hv_init.c > +++ b/arch/x86/hyperv/hv_init.c > @@ -35,7 +35,28 @@ > #include > > void *hv_hypercall_pg; > + > +#ifdef CONFIG_X86_64 > +u64 hv_pg_hypercall(u64 control, u64 param1, u64 param2) > +{ > + u64 hv_status; > + > + if (!hv_hypercall_pg) > + return U64_MAX; > + > + register u64 __r8 asm("r8") = param2; > + asm volatile (CALL_NOSPEC > + : "=a" (hv_status), ASM_CALL_CONSTRAINT, > + "+c" (control), "+d" (param1) > + : "r" (__r8), r8 is call-clobbered register, so you should use "+r" (__r8) to properly clobber it: "+c" (control), "+d" (param1), "+r" (__r8) : THUNK_TARGET(hv_hypercall_pg) > + : "cc", "memory", "r9", "r10", "r11"); > + > + return hv_status; > +} > +#else > EXPORT_SYMBOL_GPL(hv_hypercall_pg); > +#endif > > union hv_ghcb * __percpu *hv_ghcb_pg; > > --- a/arch/x86/hyperv/ivm.c > +++ b/arch/x86/hyperv/ivm.c > @@ -376,6 +376,20 @@ int hv_snp_boot_ap(u32 cpu, unsigned lon > return ret; > } > > +u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2) > +{ > + u64 hv_status; > + > + register u64 __r8 asm("r8") = param2; > + asm volatile("vmmcall" > + : "=a" (hv_status), ASM_CALL_CONSTRAINT, > + "+c" (control), "+d" (param1) > + : "r" (__r8) Also here: "+c" (control), "+d" (param1), "+r" (__r8) : > + : "cc", "memory", "r9", "r10", "r11"); > + > + return hv_status; > +} Uros.