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Message-ID: <3e81d02d2780a0636a69b948acabf4641b8c416d.1746874095.git.kai.huang@intel.com> Date: Sat, 10 May 2025 11:20:07 +0000 From: Kai Huang <kai.huang@...el.com> To: dave.hansen@...el.com, bp@...en8.de, tglx@...utronix.de, peterz@...radead.org, mingo@...hat.com Cc: kirill.shutemov@...ux.intel.com, hpa@...or.com, x86@...nel.org, linux-kernel@...r.kernel.org, pbonzini@...hat.com, seanjc@...gle.com, rick.p.edgecombe@...el.com, isaku.yamahata@...el.com, reinette.chatre@...el.com, dan.j.williams@...el.com, thomas.lendacky@....com, ashish.kalra@....com, nik.borisov@...e.com, sagis@...gle.com Subject: [PATCH v2 3/5] x86/kexec: Disable kexec/kdump on platforms with TDX partial write erratum Some early TDX-capable platforms have an erratum: A kernel partial write (a write transaction of less than cacheline lands at memory controller) to TDX private memory poisons that memory, and a subsequent read triggers a machine check. On those platforms, the old kernel must reset TDX private memory before jumping to the new kernel, otherwise the new kernel may see unexpected machine check. Currently the kernel doesn't track which page is a TDX private page. For simplicity just fail kexec/kdump for those platforms. Leverage the existing machine_kexec_prepare() to fail kexec/kdump by adding the check of the presence of the TDX erratum (which is only checked for if the kernel is built with TDX host support). This rejects kexec/kdump when the kernel is loading the kexec/kdump kernel image. The alternative is to reject kexec/kdump when the kernel is jumping to the new kernel. But for kexec this requires adding a new check (e.g., arch_kexec_allowed()) in the common code to fail kernel_kexec() at early stage. Kdump (crash_kexec()) needs similar check, but it's hard to justify because crash_kexec() is not supposed to abort. It's feasible to further relax this limitation, i.e., only fail kexec when TDX is actually enabled by the kernel. But this is still a half measure compared to resetting TDX private memory so just do the simplest thing for now. The impact to userspace is the users will get an error when loading the kexec/kdump kernel image: kexec_load failed: Operation not supported This might be confusing to the users, thus also print the reason in the dmesg: [..] kexec: not allowed on platform with tdx_pw_mce bug. Signed-off-by: Kai Huang <kai.huang@...el.com> --- arch/x86/kernel/machine_kexec_64.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c index f5a7b1894fcf..39e133dab7cb 100644 --- a/arch/x86/kernel/machine_kexec_64.c +++ b/arch/x86/kernel/machine_kexec_64.c @@ -347,6 +347,22 @@ int machine_kexec_prepare(struct kimage *image) unsigned long reloc_end = (unsigned long)__relocate_kernel_end; int result; + /* + * Some early TDX-capable platforms have an erratum. A kernel + * partial write (a write transaction of less than cacheline + * lands at memory controller) to TDX private memory poisons that + * memory, and a subsequent read triggers a machine check. + * + * On those platforms the old kernel must reset TDX private + * memory before jumping to the new kernel otherwise the new + * kernel may see unexpected machine check. For simplicity + * just fail kexec/kdump on those platforms. + */ + if (boot_cpu_has_bug(X86_BUG_TDX_PW_MCE)) { + pr_info_once("Not allowed on platform with tdx_pw_mce bug\n"); + return -EOPNOTSUPP; + } + /* Setup the identity mapped 64bit page table */ result = init_pgtable(image, __pa(control_page)); if (result) -- 2.43.0
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