[PATCH 15/24] x86/mm: Allow flushing for future ASID switches

[Ingo Molnar]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

If changing the page tables in such a way that an invalidation of
all contexts (aka. PCIDs / ASIDs) is required, they can be
actively invalidated by:

 1. INVPCID for each PCID (works for single pages too).

 2. Load CR3 with each PCID without the NOFLUSH bit set

 3. Load CR3 with the NOFLUSH bit set for each and do INVLPG for each address.

But, none of these are really feasible since there are ~6 ASIDs (12 with
KAISER) at the time that invalidation is required.  Instead of
actively invalidating them, invalidate the *current* context and
also mark the cpu_tlbstate _quickly_ to indicate future invalidation
to be required.

At the next context-switch, look for this indicator
('all_other_ctxs_invalid' being set) invalidate all of the
cpu_tlbstate.ctxs[] entries.

This ensures that any future context switches will do a full flush
of the TLB, picking up the previous changes.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: daniel.gruss@xxxxxxxxxxxxxx
Cc: hughd@xxxxxxxxxx
Cc: keescook@xxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
Cc: michael.schwarz@xxxxxxxxxxxxxx
Cc: moritz.lipp@xxxxxxxxxxxxxx
Cc: richard.fellner@xxxxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20171123003507.E8C327F5@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 arch/x86/include/asm/tlbflush.h | 47 ++++++++++++++++++++++++++++++++---------
 arch/x86/mm/tlb.c               | 35 ++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 3732b75c248a..446a4a2d4457 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -184,6 +184,17 @@ struct tlb_state {
 	 */
 	bool is_lazy;
 
+	/*
+	 * If set we changed the page tables in such a way that we
+	 * needed an invalidation of all contexts (aka. PCIDs / ASIDs).
+	 * This tells us to go invalidate all the non-loaded ctxs[]
+	 * on the next context switch.
+	 *
+	 * The current ctx was kept up-to-date as it ran and does not
+	 * need to be invalidated.
+	 */
+	bool all_other_ctxs_invalid;
+
 	/*
 	 * Access to this CR4 shadow and to H/W CR4 is protected by
 	 * disabling interrupts when modifying either one.
@@ -264,6 +275,19 @@ static inline unsigned long cr4_read_shadow(void)
 	return this_cpu_read(cpu_tlbstate.cr4);
 }
 
+static inline void tlb_flush_shared_nonglobals(void)
+{
+	/*
+	 * With global pages, all of the shared kenel page tables
+	 * are set as _PAGE_GLOBAL.  We have no shared nonglobals
+	 * and nothing to do here.
+	 */
+	if (IS_ENABLED(CONFIG_X86_GLOBAL_PAGES))
+		return;
+
+	this_cpu_write(cpu_tlbstate.all_other_ctxs_invalid, true);
+}
+
 /*
  * Save some of cr4 feature set we're using (e.g.  Pentium 4MB
  * enable and PPro Global page enable), so that any CPU's that boot
@@ -293,6 +317,10 @@ static inline void __native_flush_tlb(void)
 	preempt_disable();
 	native_write_cr3(__native_read_cr3());
 	preempt_enable();
+	/*
+	 * Does not need tlb_flush_shared_nonglobals() since the CR3 write
+	 * without PCIDs flushes all non-globals.
+	 */
 }
 
 static inline void __native_flush_tlb_global_irq_disabled(void)
@@ -338,24 +366,23 @@ static inline void __native_flush_tlb_single(unsigned long addr)
 
 static inline void __flush_tlb_all(void)
 {
-	if (boot_cpu_has(X86_FEATURE_PGE))
+	if (boot_cpu_has(X86_FEATURE_PGE)) {
 		__flush_tlb_global();
-	else
+	} else {
 		__flush_tlb();
-
-	/*
-	 * Note: if we somehow had PCID but not PGE, then this wouldn't work --
-	 * we'd end up flushing kernel translations for the current ASID but
-	 * we might fail to flush kernel translations for other cached ASIDs.
-	 *
-	 * To avoid this issue, we force PCID off if PGE is off.
-	 */
+		tlb_flush_shared_nonglobals();
+	}
 }
 
 static inline void __flush_tlb_one(unsigned long addr)
 {
 	count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
 	__flush_tlb_single(addr);
+	/*
+	 * Invalidate other address spaces inaccessible to single-page
+	 * invalidation:
+	 */
+	tlb_flush_shared_nonglobals();
 }
 
 #define TLB_FLUSH_ALL	-1UL
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index e629dbda01a0..81941f1690fa 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -28,6 +28,38 @@
  *	Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
  */
 
+/*
+ * We get here when we do something requiring a TLB invalidation
+ * but could not go invalidate all of the contexts.  We do the
+ * necessary invalidation by clearing out the 'ctx_id' which
+ * forces a TLB flush when the context is loaded.
+ */
+void clear_non_loaded_ctxs(void)
+{
+	u16 asid;
+
+	/*
+	 * This is only expected to be set if we have disabled
+	 * kernel _PAGE_GLOBAL pages.
+	 */
+	if (IS_ENABLED(CONFIG_X86_GLOBAL_PAGES)) {
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
+		/* Do not need to flush the current asid */
+		if (asid == this_cpu_read(cpu_tlbstate.loaded_mm_asid))
+			continue;
+		/*
+		 * Make sure the next time we go to switch to
+		 * this asid, we do a flush:
+		 */
+		this_cpu_write(cpu_tlbstate.ctxs[asid].ctx_id, 0);
+	}
+	this_cpu_write(cpu_tlbstate.all_other_ctxs_invalid, false);
+}
+
 atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);
 
 
@@ -42,6 +74,9 @@ static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
 		return;
 	}
 
+	if (this_cpu_read(cpu_tlbstate.all_other_ctxs_invalid))
+		clear_non_loaded_ctxs();
+
 	for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
 		if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) !=
 		    next->context.ctx_id)
-- 
2.14.1