Re: [PATCH v14 09/13] x86/mm: global ASID process exit helpers

[Borislav Petkov <bp@alien8.de>]

On Tue, Feb 25, 2025 at 10:00:44PM -0500, Rik van Riel wrote:
> A global ASID is allocated for the lifetime of a process.
> 
> Free the global ASID at process exit time.
> 
> Signed-off-by: Rik van Riel <riel@surriel.com>
> ---
>  arch/x86/include/asm/mmu_context.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)

So I don't like the ifdeffery and tried removing it, see below.

So I added helpers.

Then I entered the include hell.

And then I caught a bug with the DISABLED_FEATURE stuff.

Anyway, see below. It builds the allno-, defconfig and mine I use on this
machine so more testing is definitely needed. But the end result looks a lot
better now.

I'll integrate the other changes into the respective patches and I probably
should push my branch somewhere as we have accumulated a lot of changes by now
so tracking them over mail is getting not that easy anymore.

Will do so on Monday.

diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
index f9af51205f07..3207e5546438 100644
--- a/arch/x86/Kconfig.cpufeatures
+++ b/arch/x86/Kconfig.cpufeatures
@@ -196,6 +196,6 @@ config X86_DISABLED_FEATURE_SEV_SNP
 	def_bool y
 	depends on !KVM_AMD_SEV
 
-config X86_DISABLED_FEATURE_BROADCAST_TLB_FLUSH
+config X86_DISABLED_FEATURE_INVLPGB
 	def_bool y
 	depends on !X86_BROADCAST_TLB_FLUSH
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index a2c70e495b1b..2398058b6e83 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -2,7 +2,6 @@
 #ifndef _ASM_X86_MMU_CONTEXT_H
 #define _ASM_X86_MMU_CONTEXT_H
 
-#include <asm/desc.h>
 #include <linux/atomic.h>
 #include <linux/mm_types.h>
 #include <linux/pkeys.h>
@@ -13,6 +12,7 @@
 #include <asm/paravirt.h>
 #include <asm/debugreg.h>
 #include <asm/gsseg.h>
+#include <asm/desc.h>
 
 extern atomic64_t last_mm_ctx_id;
 
@@ -139,6 +139,9 @@ static inline void mm_reset_untag_mask(struct mm_struct *mm)
 #define enter_lazy_tlb enter_lazy_tlb
 extern void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
 
+#define mm_init_global_asid mm_init_global_asid
+extern void mm_init_global_asid(struct mm_struct *mm);
+
 extern void mm_free_global_asid(struct mm_struct *mm);
 
 /*
@@ -163,6 +166,8 @@ static inline int init_new_context(struct task_struct *tsk,
 		mm->context.execute_only_pkey = -1;
 	}
 #endif
+
+	mm_init_global_asid(mm);
 	mm_reset_untag_mask(mm);
 	init_new_context_ldt(mm);
 	return 0;
@@ -172,6 +177,7 @@ static inline int init_new_context(struct task_struct *tsk,
 static inline void destroy_context(struct mm_struct *mm)
 {
 	destroy_context_ldt(mm);
+	mm_free_global_asid(mm);
 }
 
 extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 37b735dcf025..01d8a152f04a 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -261,6 +261,14 @@ static inline u16 mm_global_asid(struct mm_struct *mm)
 	return asid;
 }
 
+static inline void mm_init_global_asid(struct mm_struct *mm)
+{
+	if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
+		mm->context.global_asid = 0;
+		mm->context.asid_transition = false;
+	}
+}
+
 static inline void mm_assign_global_asid(struct mm_struct *mm, u16 asid)
 {
 	/*
@@ -272,7 +280,7 @@ static inline void mm_assign_global_asid(struct mm_struct *mm, u16 asid)
 	smp_store_release(&mm->context.global_asid, asid);
 }
 
-static inline bool in_asid_transition(struct mm_struct *mm)
+static inline bool mm_in_asid_transition(struct mm_struct *mm)
 {
 	if (!cpu_feature_enabled(X86_FEATURE_INVLPGB))
 		return false;
@@ -280,19 +288,10 @@ static inline bool in_asid_transition(struct mm_struct *mm)
 	return mm && READ_ONCE(mm->context.asid_transition);
 }
 #else
-static inline u16 mm_global_asid(struct mm_struct *mm)
-{
-	return 0;
-}
-
-static inline void mm_assign_global_asid(struct mm_struct *mm, u16 asid)
-{
-}
-
-static inline bool in_asid_transition(struct mm_struct *mm)
-{
-	return false;
-}
+static inline u16 mm_global_asid(struct mm_struct *mm) { return 0; }
+static inline void mm_init_global_asid(struct mm_struct *mm) { }
+static inline void mm_assign_global_asid(struct mm_struct *mm, u16 asid) { }
+static inline bool mm_in_asid_transition(struct mm_struct *mm) { return false; }
 #endif
 
 #ifdef CONFIG_PARAVIRT
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index cb43ab08ea4a..c2167b331bbe 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -396,6 +396,9 @@ static void use_global_asid(struct mm_struct *mm)
 
 void mm_free_global_asid(struct mm_struct *mm)
 {
+	if (!cpu_feature_enabled(X86_FEATURE_INVLPGB))
+		return;
+
 	if (!mm_global_asid(mm))
 		return;
 
@@ -1161,7 +1164,7 @@ STATIC_NOPV void native_flush_tlb_multi(const struct cpumask *cpumask,
 	 * up on the new contents of what used to be page tables, while
 	 * doing a speculative memory access.
 	 */
-	if (info->freed_tables || in_asid_transition(info->mm))
+	if (info->freed_tables || mm_in_asid_transition(info->mm))
 		on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
 	else
 		on_each_cpu_cond_mask(should_flush_tlb, flush_tlb_func,
-- 
2.43.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette