linux-kernel - [RFC PATCH v0 3/6] x86: Enable Upper Address Ignore(UAI) feature

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Date:   Thu, 10 Mar 2022 16:45:42 +0530
From:   Bharata B Rao <bharata@....com>
To:     <linux-kernel@...r.kernel.org>
CC:     <linux-mm@...ck.org>, <x86@...nel.org>,
        <kirill.shutemov@...ux.intel.com>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
        <catalin.marinas@....com>, <will@...nel.org>, <shuah@...nel.org>,
        <oleg@...hat.com>, <ananth.narayan@....com>,
        "Bharata B Rao" <bharata@....com>
Subject: [RFC PATCH v0 3/6] x86: Enable Upper Address Ignore(UAI) feature

UAI feature is enabled by setting bit 20 in EFER MSR.

Signed-off-by: Bharata B Rao <bharata@....com>
---
 arch/x86/include/asm/msr-index.h | 2 ++
 arch/x86/kernel/setup.c          | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index a4a39c3e0f19..ce763952278f 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -30,6 +30,7 @@
 #define _EFER_SVME		12 /* Enable virtualization */
 #define _EFER_LMSLE		13 /* Long Mode Segment Limit Enable */
 #define _EFER_FFXSR		14 /* Enable Fast FXSAVE/FXRSTOR */
+#define _EFER_UAI		20 /* Enable Upper Address Ignore */
 
 #define EFER_SCE		(1<<_EFER_SCE)
 #define EFER_LME		(1<<_EFER_LME)
@@ -38,6 +39,7 @@
 #define EFER_SVME		(1<<_EFER_SVME)
 #define EFER_LMSLE		(1<<_EFER_LMSLE)
 #define EFER_FFXSR		(1<<_EFER_FFXSR)
+#define EFER_UAI		(1<<_EFER_UAI)
 
 /* Intel MSRs. Some also available on other CPUs */
 
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index f7a132eb794d..12615b1b4af5 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -740,6 +740,12 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
 	return 0;
 }
 
+static inline void __init uai_enable(void)
+{
+	if (boot_cpu_has(X86_FEATURE_UAI))
+		msr_set_bit(MSR_EFER, _EFER_UAI);
+}
+
 /*
  * Determine if we were loaded by an EFI loader.  If so, then we have also been
  * passed the efi memmap, systab, etc., so we should use these data structures
@@ -1146,6 +1152,8 @@ void __init setup_arch(char **cmdline_p)
 
 	x86_init.paging.pagetable_init();
 
+	uai_enable();
+
 	kasan_init();
 
 	/*
-- 
2.25.1