Revert "FROMLIST: arm64: Disable TTBR0_EL1 during normal kernel execution"

This reverts commit 5775ca34829caf0664c8ccc02fd0e93cb6022e0f.

Bug: 31432001
Change-Id: I9b07c2f01bc2bcfed51f60ab487034639f5e1960
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

3 files changed, 15 insertions, 64 deletions

diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index 932f5a56d1a6..8e88a696c9cb 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -1,7 +1,6 @@
 #ifndef _ASM_EFI_H
 #define _ASM_EFI_H
 
-#include <asm/cpufeature.h>
 #include <asm/io.h>
 #include <asm/mmu_context.h>
 #include <asm/neon.h>
@@ -70,30 +69,7 @@ int efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md);
 
 static inline void efi_set_pgd(struct mm_struct *mm)
 {
-	__switch_mm(mm);
-
-	if (system_uses_ttbr0_pan()) {
-		if (mm != current->active_mm) {
-			/*
-			 * Update the current thread's saved ttbr0 since it is
-			 * restored as part of a return from exception. Set
-			 * the hardware TTBR0_EL1 using cpu_switch_mm()
-			 * directly to enable potential errata workarounds.
-			 */
-			update_saved_ttbr0(current, mm);
-			cpu_switch_mm(mm->pgd, mm);
-		} else {
-			/*
-			 * Defer the switch to the current thread's TTBR0_EL1
-			 * until uaccess_enable(). Restore the current
-			 * thread's saved ttbr0 corresponding to its active_mm
-			 * (if different from init_mm).
-			 */
-			cpu_set_reserved_ttbr0();
-			if (current->active_mm != &init_mm)
-				update_saved_ttbr0(current, current->active_mm);
-		}
-	}
+	switch_mm(NULL, mm, NULL);
 }
 
 void efi_virtmap_load(void);
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 4a32fd5f101d..a00f7cf35bbd 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -23,7 +23,6 @@
 #include <linux/sched.h>
 
 #include <asm/cacheflush.h>
-#include <asm/cpufeature.h>
 #include <asm/proc-fns.h>
 #include <asm-generic/mm_hooks.h>
 #include <asm/cputype.h>
@@ -114,7 +113,7 @@ static inline void cpu_uninstall_idmap(void)
 	local_flush_tlb_all();
 	cpu_set_default_tcr_t0sz();
 
-	if (mm != &init_mm && !system_uses_ttbr0_pan())
+	if (mm != &init_mm)
 		cpu_switch_mm(mm->pgd, mm);
 }
 
@@ -174,27 +173,21 @@ enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
 {
 }
 
-#ifdef CONFIG_ARM64_SW_TTBR0_PAN
-static inline void update_saved_ttbr0(struct task_struct *tsk,
-				      struct mm_struct *mm)
-{
-	if (system_uses_ttbr0_pan()) {
-		BUG_ON(mm->pgd == swapper_pg_dir);
-		task_thread_info(tsk)->ttbr0 =
-			virt_to_phys(mm->pgd) | ASID(mm) << 48;
-	}
-}
-#else
-static inline void update_saved_ttbr0(struct task_struct *tsk,
-				      struct mm_struct *mm)
-{
-}
-#endif
-
-static inline void __switch_mm(struct mm_struct *next)
+/*
+ * This is the actual mm switch as far as the scheduler
+ * is concerned.  No registers are touched.  We avoid
+ * calling the CPU specific function when the mm hasn't
+ * actually changed.
+ */
+static inline void
+switch_mm(struct mm_struct *prev, struct mm_struct *next,
+	  struct task_struct *tsk)
 {
 	unsigned int cpu = smp_processor_id();
 
+	if (prev == next)
+		return;
+
 	/*
 	 * init_mm.pgd does not contain any user mappings and it is always
 	 * active for kernel addresses in TTBR1. Just set the reserved TTBR0.
@@ -207,23 +200,7 @@ static inline void __switch_mm(struct mm_struct *next)
 	check_and_switch_context(next, cpu);
 }
 
-static inline void
-switch_mm(struct mm_struct *prev, struct mm_struct *next,
-	  struct task_struct *tsk)
-{
-	if (prev != next)
-		__switch_mm(next);
-
-	/*
-	 * Update the saved TTBR0_EL1 of the scheduled-in task as the previous
-	 * value may have not been initialised yet (activate_mm caller) or the
-	 * ASID has changed since the last run (following the context switch
-	 * of another thread of the same process).
-	 */
-	update_saved_ttbr0(tsk, next);
-}
-
 #define deactivate_mm(tsk,mm)	do { } while (0)
-#define activate_mm(prev,next)	switch_mm(prev, next, current)
+#define activate_mm(prev,next)	switch_mm(prev, next, NULL)
 
 #endif
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 5eedfd83acc7..1528d52eb8c0 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -21,8 +21,6 @@
 
 #include <uapi/asm/ptrace.h>
 
-#define _PSR_PAN_BIT		22
-
 /* Current Exception Level values, as contained in CurrentEL */
 #define CurrentEL_EL1		(1 << 2)
 #define CurrentEL_EL2		(2 << 2)