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X-CSE-ConnectionGUID: viRKRnImSliMZ/21pju8+w== X-CSE-MsgGUID: iLnZQi/PQpubM9KJRix73A== X-IronPort-AV: E=McAfee;i="6800,10657,11692"; a="71549231" X-IronPort-AV: E=Sophos;i="6.21,274,1763452800"; d="scan'208";a="71549231" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2026 08:10:16 -0800 X-CSE-ConnectionGUID: Vyls9xQeSZuLf00A9ztyOQ== X-CSE-MsgGUID: f49i3fagTOaNrMxJeaoKzw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,274,1763452800"; d="scan'208";a="210483918" Received: from tfalcon-desk.amr.corp.intel.com (HELO [10.125.111.86]) ([10.125.111.86]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2026 08:10:15 -0800 Message-ID: <9c8c2d69-5434-4416-ba37-897ce00e2b11@intel.com> Date: Thu, 5 Feb 2026 08:10:14 -0800 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] x86/fred: Fix early boot failures on SEV-ES/SNP guests To: Nikunj A Dadhania , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, bp@alien8.de, thomas.lendacky@amd.com Cc: tglx@kernel.org, mingo@redhat.com, dave.hansen@linux.intel.com, hpa@zytor.com, xin@zytor.com, seanjc@google.com, pbonzini@redhat.com, x86@kernel.org, jon.grimm@amd.com, stable@vger.kernel.org References: <20260205051030.1225975-1-nikunj@amd.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/4/26 21:10, Nikunj A Dadhania wrote: ... > --- a/arch/x86/entry/entry_fred.c > +++ b/arch/x86/entry/entry_fred.c > @@ -208,6 +208,11 @@ static noinstr void fred_hwexc(struct pt_regs *regs, unsigned long error_code) > #ifdef CONFIG_X86_CET > case X86_TRAP_CP: return exc_control_protection(regs, error_code); > #endif > + case X86_TRAP_VC: > + if (user_mode(regs)) > + return user_exc_vmm_communication(regs, error_code); > + else > + return kernel_exc_vmm_communication(regs, error_code); > default: return fred_bad_type(regs, error_code); > } Please look at the code in the ~20 lines above this hunk. It has a nice, consistent form of: case X86_TRAP_FOO: return exc_foo_action(...); Could we keep that going, please? Second, these functions are defined in arch/x86/coco/sev/vc-handle.c. That looks suspiciously like CONFIG_AMD_MEM_ENCRYPT code and not something that will compile everywhere. Also note the other features in the switch() block. See all the #ifdefs on those? Have you compiled this? > diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c > index e736b19e18de..8cf4da546a8e 100644 > --- a/arch/x86/kernel/fred.c > +++ b/arch/x86/kernel/fred.c > @@ -27,9 +27,6 @@ EXPORT_PER_CPU_SYMBOL(fred_rsp0); > > void cpu_init_fred_exceptions(void) > { > - /* When FRED is enabled by default, remove this log message */ > - pr_info("Initialize FRED on CPU%d\n", smp_processor_id()); > - > /* > * If a kernel event is delivered before a CPU goes to user level for > * the first time, its SS is NULL thus NULL is pushed into the SS field > @@ -70,6 +67,17 @@ void cpu_init_fred_exceptions(void) > /* Use int $0x80 for 32-bit system calls in FRED mode */ > setup_clear_cpu_cap(X86_FEATURE_SYSFAST32); > setup_clear_cpu_cap(X86_FEATURE_SYSCALL32); > + > + /* > + * For secondary processors, FRED bit in CR4 gets enabled in cr4_init() > + * and FRED MSRs are not configured till the end of this function. For > + * SEV-ES and SNP guests, any console write before the FRED MSRs are > + * setup will cause a #VC and cannot be handled. Move the pr_info to > + * the end of this function. > + * > + * When FRED is enabled by default, remove this log message > + */ > + pr_info("Initialized FRED on CPU%d\n", smp_processor_id()); > } This seems really gross. Now there's a window where printk() doesn't work. To fix it, we start moving printk()'s? Please, no. Shouldn't we flip the FRED CR4 bit _last_, once all the MSRs are set up? Why is it backwards in the first place? Why can't it be fixed?