linux-kernel - [RFC PATCH 14/47] mm: asi: Disable ASI API when ASI is not enabled for a process

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Date:   Tue, 22 Feb 2022 21:21:50 -0800
From:   Junaid Shahid <junaids@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     kvm@...r.kernel.org, pbonzini@...hat.com, jmattson@...gle.com,
        pjt@...gle.com, oweisse@...gle.com, alexandre.chartre@...cle.com,
        rppt@...ux.ibm.com, dave.hansen@...ux.intel.com,
        peterz@...radead.org, tglx@...utronix.de, luto@...nel.org,
        linux-mm@...ck.org
Subject: [RFC PATCH 14/47] mm: asi: Disable ASI API when ASI is not enabled
 for a process

If ASI is not enabled for a process, then asi_init() will return a NULL
ASI pointer as output, though it will return a 0 error code. All other
ASI API functions will return without an error when they get a NULL ASI
pointer.

Signed-off-by: Junaid Shahid <junaids@...gle.com>


---
 arch/x86/include/asm/asi.h |  2 +-
 arch/x86/mm/asi.c          | 18 ++++++++++--------
 include/asm-generic/asi.h  |  7 ++++++-
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/asi.h b/arch/x86/include/asm/asi.h
index 64c2b4d1dba2..f69e1f2f09a4 100644
--- a/arch/x86/include/asm/asi.h
+++ b/arch/x86/include/asm/asi.h
@@ -51,7 +51,7 @@ int  asi_register_class(const char *name, uint flags,
 			const struct asi_hooks *ops);
 void asi_unregister_class(int index);
 
-int  asi_init(struct mm_struct *mm, int asi_index);
+int  asi_init(struct mm_struct *mm, int asi_index, struct asi **out_asi);
 void asi_destroy(struct asi *asi);
 
 void asi_enter(struct asi *asi);
diff --git a/arch/x86/mm/asi.c b/arch/x86/mm/asi.c
index ca50a32ecd7e..58d1c532274a 100644
--- a/arch/x86/mm/asi.c
+++ b/arch/x86/mm/asi.c
@@ -207,11 +207,13 @@ static int __init asi_global_init(void)
 }
 subsys_initcall(asi_global_init)
 
-int asi_init(struct mm_struct *mm, int asi_index)
+int asi_init(struct mm_struct *mm, int asi_index, struct asi **out_asi)
 {
 	struct asi *asi = &mm->asi[asi_index];
 
-	if (!boot_cpu_has(X86_FEATURE_ASI))
+	*out_asi = NULL;
+
+	if (!boot_cpu_has(X86_FEATURE_ASI) || !mm->asi_enabled)
 		return 0;
 
 	/* Index 0 is reserved for special purposes. */
@@ -238,13 +240,15 @@ int asi_init(struct mm_struct *mm, int asi_index)
 			set_pgd(asi->pgd + i, asi_global_nonsensitive_pgd[i]);
 	}
 
+	*out_asi = asi;
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(asi_init);
 
 void asi_destroy(struct asi *asi)
 {
-	if (!boot_cpu_has(X86_FEATURE_ASI))
+	if (!boot_cpu_has(X86_FEATURE_ASI) || !asi)
 		return;
 
 	asi_free_pgd(asi);
@@ -278,11 +282,9 @@ void __asi_enter(void)
 
 void asi_enter(struct asi *asi)
 {
-	if (!static_cpu_has(X86_FEATURE_ASI))
+	if (!static_cpu_has(X86_FEATURE_ASI) || !asi)
 		return;
 
-	VM_WARN_ON_ONCE(!asi);
-
 	this_cpu_write(asi_cpu_state.target_asi, asi);
 	barrier();
 
@@ -423,7 +425,7 @@ int asi_map_gfp(struct asi *asi, void *addr, size_t len, gfp_t gfp_flags)
 	size_t end = start + len;
 	size_t page_size;
 
-	if (!static_cpu_has(X86_FEATURE_ASI))
+	if (!static_cpu_has(X86_FEATURE_ASI) || !asi)
 		return 0;
 
 	VM_BUG_ON(start & ~PAGE_MASK);
@@ -514,7 +516,7 @@ void asi_unmap(struct asi *asi, void *addr, size_t len, bool flush_tlb)
 	size_t end = start + len;
 	pgtbl_mod_mask mask = 0;
 
-	if (!static_cpu_has(X86_FEATURE_ASI) || !len)
+	if (!static_cpu_has(X86_FEATURE_ASI) || !asi || !len)
 		return;
 
 	VM_BUG_ON(start & ~PAGE_MASK);
diff --git a/include/asm-generic/asi.h b/include/asm-generic/asi.h
index f918cd052722..51c9c4a488e8 100644
--- a/include/asm-generic/asi.h
+++ b/include/asm-generic/asi.h
@@ -33,7 +33,12 @@ static inline void asi_unregister_class(int asi_index) { }
 
 static inline void asi_init_mm_state(struct mm_struct *mm) { }
 
-static inline int asi_init(struct mm_struct *mm, int asi_index) { return 0; }
+static inline
+int asi_init(struct mm_struct *mm, int asi_index, struct asi **out_asi)
+{
+	*out_asi = NULL;
+	return 0;
+}
 
 static inline void asi_destroy(struct asi *asi) { }
 
-- 
2.35.1.473.g83b2b277ed-goog