linux-kernel - [PATCH 1/4] X86: Update mmu_cr4_features during feature identification

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Message-Id: <20200617190757.27081-2-john.s.andersen@intel.com>
Date:   Wed, 17 Jun 2020 12:07:54 -0700
From:   John Andersen <john.s.andersen@...el.com>
To:     corbet@....net, pbonzini@...hat.com, tglx@...utronix.de,
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Subject: [PATCH 1/4] X86: Update mmu_cr4_features during feature identification

In identify_cpu when setting up SMEP/SMAP/UMIP call
cr4_set_bits_and_update_boot instead of cr4_set_bits. This ensures that
mmu_cr4_features contains those bits, and does not disable those
protections when in hibernation asm.

setup_arch updates mmu_cr4_features to save what identified features are
supported for later use in hibernation asm when cr4 needs to be modified
to toggle PGE. cr4 writes happen in restore_image and restore_registers.
setup_arch occurs before identify_cpu, this leads to mmu_cr4_features
not containing some of the cr4 features which were enabled via
identify_cpu when hibernation asm is executed.

On CPU bringup when cr4_set_bits_and_update_boot is called
mmu_cr4_features will now be written to. For the boot CPU,
the __ro_after_init on mmu_cr4_features does not cause a fault. However,
__ro_after_init was removed due to it triggering faults on non-boot
CPUs.

Signed-off-by: John Andersen <john.s.andersen@...el.com>
---
 arch/x86/kernel/cpu/common.c | 6 +++---
 arch/x86/kernel/setup.c      | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d07809286b95..921e67086a00 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -297,7 +297,7 @@ __setup("nosmep", setup_disable_smep);
 static __always_inline void setup_smep(struct cpuinfo_x86 *c)
 {
 	if (cpu_has(c, X86_FEATURE_SMEP))
-		cr4_set_bits(X86_CR4_SMEP);
+		cr4_set_bits_and_update_boot(X86_CR4_SMEP);
 }
 
 static __init int setup_disable_smap(char *arg)
@@ -316,7 +316,7 @@ static __always_inline void setup_smap(struct cpuinfo_x86 *c)
 
 	if (cpu_has(c, X86_FEATURE_SMAP)) {
 #ifdef CONFIG_X86_SMAP
-		cr4_set_bits(X86_CR4_SMAP);
+		cr4_set_bits_and_update_boot(X86_CR4_SMAP);
 #else
 		cr4_clear_bits(X86_CR4_SMAP);
 #endif
@@ -333,7 +333,7 @@ static __always_inline void setup_umip(struct cpuinfo_x86 *c)
 	if (!cpu_has(c, X86_FEATURE_UMIP))
 		goto out;
 
-	cr4_set_bits(X86_CR4_UMIP);
+	cr4_set_bits_and_update_boot(X86_CR4_UMIP);
 
 	pr_info_once("x86/cpu: User Mode Instruction Prevention (UMIP) activated\n");
 
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index a3767e74c758..d9c678b37a9b 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -138,9 +138,9 @@ EXPORT_SYMBOL(boot_cpu_data);
 
 
 #if !defined(CONFIG_X86_PAE) || defined(CONFIG_X86_64)
-__visible unsigned long mmu_cr4_features __ro_after_init;
+__visible unsigned long mmu_cr4_features;
 #else
-__visible unsigned long mmu_cr4_features __ro_after_init = X86_CR4_PAE;
+__visible unsigned long mmu_cr4_features = X86_CR4_PAE;
 #endif
 
 /* Boot loader ID and version as integers, for the benefit of proc_dointvec */
-- 
2.21.0