linux-kernel - Re: [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is active

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Message-ID: <20170915122430.pnroy6vsg53warel@pd.tnic>
Date:   Fri, 15 Sep 2017 14:24:30 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        David Laight <David.Laight@...lab.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        David Howells <dhowells@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Christoph Lameter <cl@...ux.com>,
        Jonathan Corbet <corbet@....net>,
        Radim Krcmár <rkrcmar@...hat.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Laura Abbott <labbott@...hat.com>,
        Tony Luck <tony.luck@...el.com>, Ard.Biesheuvel@...or.com
Subject: Re: [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is
 active

On Tue, Aug 22, 2017 at 06:52:48PM +0200, Borislav Petkov wrote:
> As always, the devil is in the detail.

Ok, actually we can make this much simpler by using a static key. A
conceptual patch below - I only need to fix that crazy include hell I'm
stepping into with this.

In any case, we were talking about having a static branch already so
this fits the whole strategy.

---
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index d174b1c4a99e..e45369158632 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -45,6 +45,8 @@ EXPORT_SYMBOL_GPL(sme_me_mask);
 unsigned int sev_enabled __section(.data) = 0;
 EXPORT_SYMBOL_GPL(sev_enabled);
 
+DEFINE_STATIC_KEY_FALSE(__sev);
+
 /* Buffer used for early in-place encryption by BSP, no locking needed */
 static char sme_early_buffer[PAGE_SIZE] __aligned(PAGE_SIZE);
 
@@ -790,6 +792,7 @@ void __init __nostackprotector sme_enable(struct boot_params *bp)
 		/* SEV state cannot be controlled by a command line option */
 		sme_me_mask = me_mask;
 		sev_enabled = 1;
+		static_branch_enable(&__sev);
 		return;
 	}
 
diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
index ea0831a8dbe2..f3ab965a3d6a 100644
--- a/include/linux/mem_encrypt.h
+++ b/include/linux/mem_encrypt.h
@@ -13,6 +13,8 @@
 #ifndef __MEM_ENCRYPT_H__
 #define __MEM_ENCRYPT_H__
 
+#include <linux/jump_label.h>
+
 #ifndef __ASSEMBLY__
 
 #ifdef CONFIG_ARCH_HAS_MEM_ENCRYPT
@@ -26,6 +28,8 @@
 
 #endif	/* CONFIG_ARCH_HAS_MEM_ENCRYPT */
 
+extern struct static_key_false __sev;
+
 static inline bool sme_active(void)
 {
 	return (sme_me_mask && !sev_enabled);
@@ -33,7 +37,7 @@ static inline bool sme_active(void)
 
 static inline bool sev_active(void)
 {
-	return (sme_me_mask && sev_enabled);
+	return static_branch_unlikely(&__sev);
 }
 
 static inline unsigned long sme_get_me_mask(void)

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--