linux-kernel - Re: [PATCH v2 09/12] x86/sev: Use AP Jump Table blob to stop CPU

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Date:   Mon, 15 Nov 2021 19:44:14 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Joerg Roedel <joro@...tes.org>
Cc:     x86@...nel.org, Eric Biederman <ebiederm@...ssion.com>,
        kexec@...ts.infradead.org, Joerg Roedel <jroedel@...e.de>,
        hpa@...or.com, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Martin Radev <martin.b.radev@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v2 09/12] x86/sev: Use AP Jump Table blob to stop CPU

On Mon, Sep 13, 2021 at 05:56:00PM +0200, Joerg Roedel wrote:
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 134a7c9d91b6..cd14b6e10f12 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -81,12 +81,19 @@ static __always_inline void sev_es_nmi_complete(void)
>  		__sev_es_nmi_complete();
>  }
>  extern int __init sev_es_efi_map_ghcbs(pgd_t *pgd);
> +void __sev_es_stop_this_cpu(void);
> +static __always_inline void sev_es_stop_this_cpu(void)

What's that for?

IOW, the below seems to build too:

---
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 1f16fc907636..398105580862 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -87,12 +87,7 @@ extern enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
 					  struct es_em_ctxt *ctxt,
 					  u64 exit_code, u64 exit_info_1,
 					  u64 exit_info_2);
-void __sev_es_stop_this_cpu(void);
-static __always_inline void sev_es_stop_this_cpu(void)
-{
-	if (static_branch_unlikely(&sev_es_enable_key))
-		__sev_es_stop_this_cpu();
-}
+void sev_es_stop_this_cpu(void);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 39378357dc5a..7a74b3273f1a 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -694,8 +694,11 @@ void __noreturn sev_jumptable_ap_park(void)
 }
 STACK_FRAME_NON_STANDARD(sev_jumptable_ap_park);
 
-void __sev_es_stop_this_cpu(void)
+void sev_es_stop_this_cpu(void)
 {
+	if (!static_branch_unlikely(&sev_es_enable_key))
+		return;
+
 	/* Only park in the AP Jump Table when the code has been installed */
 	if (!sev_ap_jumptable_blob_installed)
 		return;

---

And as previously mentioned s/sev_es/sev/ if those are going to be used
on SNP guests too.

-- 
Regards/Gruss,
    Boris.

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