Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   KarimAllah Ahmed <karahmed@amazon.de>
To:     linux-kernel@vger.kernel.org
Cc:     KarimAllah Ahmed <karahmed@amazon.de>,
        Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, kvm@vger.kernel.org,
        x86@kernel.org
Subject: [RFC 06/10] x86/speculation: Add inlines to control Indirect Branch Speculation
Date:   Sat, 20 Jan 2018 20:22:57 +0100
Message-Id: <1516476182-5153-7-git-send-email-karahmed@amazon.de>
In-Reply-To: <1516476182-5153-1-git-send-email-karahmed@amazon.de>
References: <1516476182-5153-1-git-send-email-karahmed@amazon.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Thomas Gleixner <tglx@linutronix.de>

XX: I am utterly unconvinced that having "friendly, self-explanatory"
    names for the IBRS-frobbing inlines is useful. There be dragons
    here for anyone who isn't intimately familiar with what's going
    on, and it's almost better to just call it IBRS, put a reference
    to the spec, and have a clear "you must be →this← tall to ride."

[karahmed: switch to using ALTERNATIVES instead of static_cpu_has]
[dwmw2: wrmsr args inside the ALTERNATIVE again, bikeshed naming]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/include/asm/nospec-branch.h | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 8759449..5be3443 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -232,5 +232,41 @@ static inline void indirect_branch_prediction_barrier(void)
 		     : "memory");
 }
 
+/*
+ * This also performs a barrier, and setting it again when it was already
+ * set is NOT a no-op.
+ */
+static inline void restrict_branch_speculation(void)
+{
+	unsigned long ax, cx, dx;
+
+	asm volatile(ALTERNATIVE("",
+				 "movl %[msr], %%ecx\n\t"
+				 "movl %[val], %%eax\n\t"
+				 "movl $0, %%edx\n\t"
+				 "wrmsr",
+				 X86_FEATURE_IBRS)
+		     : "=a" (ax), "=c" (cx), "=d" (dx)
+		     : [msr] "i" (MSR_IA32_SPEC_CTRL),
+		       [val] "i" (SPEC_CTRL_IBRS)
+		     : "memory");
+}
+
+static inline void unrestrict_branch_speculation(void)
+{
+	unsigned long ax, cx, dx;
+
+	asm volatile(ALTERNATIVE("",
+				 "movl %[msr], %%ecx\n\t"
+				 "movl %[val], %%eax\n\t"
+				 "movl $0, %%edx\n\t"
+				 "wrmsr",
+				 X86_FEATURE_IBRS)
+		     : "=a" (ax), "=c" (cx), "=d" (dx)
+		     : [msr] "i" (MSR_IA32_SPEC_CTRL),
+		       [val] "i" (0)
+		     : "memory");
+}
+
 #endif /* __ASSEMBLY__ */
 #endif /* __NOSPEC_BRANCH_H__ */
-- 
2.7.4