linux-kernel - Re: [PATCH 1/4] x86/coco: Add a new CC attribute to unify cache flush during kexec

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Date: Wed, 21 Feb 2024 10:28:56 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tom Lendacky <thomas.lendacky@....com>, Dave Young <dyoung@...hat.com>
Cc: "Huang, Kai" <kai.huang@...el.com>, "Gao, Chao" <chao.gao@...el.com>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	"luto@...nel.org" <luto@...nel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"nik.borisov@...e.com" <nik.borisov@...e.com>,
	"bhe@...hat.com" <bhe@...hat.com>
Subject: Re: [PATCH 1/4] x86/coco: Add a new CC attribute to unify cache
 flush during kexec

On Tue, Feb 20, 2024 at 04:30:13PM -0600, Tom Lendacky wrote:
> I believe the issues were that different Intel systems would hang or reset
> and it was bisected to that commit that added the WBINVD. It was a while
> ago, but I remember that they were similar to what the 1f5e7eb7868e commit
> ended up fixing, which was debugged because sometimes the WBINVD was still
> occasionally issued resulting in the following patch
> 
>   9b040453d444 ("x86/smp: Dont access non-existing CPUID leaf")
> 
> It just means that if we go to an unconditional WBINVD, then we need to be
> careful.

Let's try it.

Dave, do you remember what issues

  f23d74f6c66c ("x86/mm: Rework wbinvd, hlt operation in stop_this_cpu()")

fixed?

If so, can you try the below diff ontop of latest tip/master to see if
those issues would reappear?

Thx.

---

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ab49ade31b0d..ec4dcc9f70ca 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -824,8 +824,7 @@ void __noreturn stop_this_cpu(void *dummy)
 	 * Test the CPUID bit directly because the machine might've cleared
 	 * X86_FEATURE_SME due to cmdline options.
 	 */
-	if (c->extended_cpuid_level >= 0x8000001f && (cpuid_eax(0x8000001f) & BIT(0)))
-		native_wbinvd();
+	native_wbinvd();
 
 	/*
 	 * This brings a cache line back and dirties it, but

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette