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Wed, 20 Aug 2025 02:51:30 -0700 (PDT) Received: from [192.168.1.84] ([93.56.169.94]) by smtp.googlemail.com with ESMTPSA id ffacd0b85a97d-3c3e673ab01sm576512f8f.18.2025.08.20.02.51.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Aug 2025 02:51:30 -0700 (PDT) Message-ID: <78253405-bff8-476c-a505-3737a499151b@redhat.com> Date: Wed, 20 Aug 2025 11:51:28 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 7/7] KVM: TDX: Explicitly do WBINVD when no more TDX SEAMCALLs To: "Huang, Kai" , "seanjc@google.com" Cc: "kvm@vger.kernel.org" , "ashish.kalra@amd.com" , "Hansen, Dave" , "thomas.lendacky@amd.com" , "kas@kernel.org" , "Chatre, Reinette" , "dwmw@amazon.co.uk" , "linux-kernel@vger.kernel.org" , "mingo@redhat.com" , "Yamahata, Isaku" , "nik.borisov@suse.com" , "tglx@linutronix.de" , "hpa@zytor.com" , "peterz@infradead.org" , "sagis@google.com" , "Chen, Farrah" , "Edgecombe, Rick P" , "bp@alien8.de" , "binbin.wu@linux.intel.com" , "Gao, Chao" , "Williams, Dan J" , "x86@kernel.org" References: From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 8/19/25 23:53, Huang, Kai wrote: > On Tue, 2025-08-19 at 12:31 +0200, Paolo Bonzini wrote: >> 2) ... but anyway, KVM is the wrong place to do the test. If anything, >> since we need a v7 to change the unnecessary stub, you could move that >> stub under #ifndef CONFIG_KEXEC_CORE and rename the function to >> tdx_cpu_flush_cache_for_kexec(). > > Agreed on renaming to tdx_cpu_flush_cache_for_kexec(). > > But with the "for_kexec()" part in the function name, it already implies > it is related to kexec, and I kinda think there's no need to test > IS_ENABLED(CONFIG_KEXEC_CORE) anymore. > > One of the main purpose of this series is to unblock TDX_HOST and KEXEC in > the Kconfig, since otherwise I've been told distros will simply choose to > disable TDX_HOST in the Kconfig. So in reality, I suppose they will be on > together probably in like 95% cases, if not 100%. > > If we want to test CONFIG_KEXEC_CORE in tdx_cpu_flush_cache_for_kexec(), > then it would be a little bit weird that why we don't test it in other > places, e.g., when setting up the boolean. Testing it in all places would > make the code unnecessarily long and harder to read. No I don't mean testing it there, but just making tdx_cpu_flush_cache_for_kexec() a stub when CONFIG_KEXEC_CORE is undefined: diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h index e9a213582f03..913199b1954b 100644 --- a/arch/x86/include/asm/tdx.h +++ b/arch/x86/include/asm/tdx.h @@ -217,7 +217,6 @@ u64 tdh_mem_page_remove(struct tdx_td *td, u64 gpa, u64 level, u64 *ext_err1, u6 u64 tdh_phymem_cache_wb(bool resume); u64 tdh_phymem_page_wbinvd_tdr(struct tdx_td *td); u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page); -void tdx_cpu_flush_cache(void); #else static inline void tdx_init(void) { } static inline int tdx_cpu_enable(void) { return -ENODEV; } @@ -225,8 +224,13 @@ static inline int tdx_enable(void) { return -ENODEV; } static inline u32 tdx_get_nr_guest_keyids(void) { return 0; } static inline const char *tdx_dump_mce_info(struct mce *m) { return NULL; } static inline const struct tdx_sys_info *tdx_get_sysinfo(void) { return NULL; } -static inline void tdx_cpu_flush_cache(void) { } #endif /* CONFIG_INTEL_TDX_HOST */ +#ifdef CONFIG_KEXEC_CORE +void tdx_cpu_flush_cache_for_kexec(void); +#else +static inline void tdx_cpu_flush_cache_for_kexec(void) { } +#endif + #endif /* !__ASSEMBLER__ */ #endif /* _ASM_X86_TDX_H */ diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 93477233baae..376d49ef4472 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -453,7 +453,7 @@ void tdx_disable_virtualization_cpu(void) * remote CPUs to stop them. Doing WBINVD in stop_this_cpu() * could potentially increase the possibility of the "race". */ - tdx_cpu_flush_cache(); + tdx_cpu_flush_cache_for_kexec(); } #define TDX_SEAMCALL_RETRIES 10000 diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c index c26e2e07ff6b..cd2a36dbbfc5 100644 --- a/arch/x86/virt/vmx/tdx/tdx.c +++ b/arch/x86/virt/vmx/tdx/tdx.c @@ -1871,7 +1871,7 @@ u64 tdh_phymem_page_wbinvd_hkid(u64 hkid, struct page *page) } EXPORT_SYMBOL_GPL(tdh_phymem_page_wbinvd_hkid); -void tdx_cpu_flush_cache(void) +void tdx_cpu_flush_cache_for_kexec(void) { lockdep_assert_preemption_disabled(); @@ -1881,4 +1881,4 @@ void tdx_cpu_flush_cache(void) wbinvd(); this_cpu_write(cache_state_incoherent, false); } -EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache); +EXPORT_SYMBOL_GPL(tdx_cpu_flush_cache_for_kexec); Personally, I'm totally okay with v6. But the above change seems to me like the best way to obey Sean's objection, better than adding the test in KVM. Paolo