From: Hugh Dickins <hughd@google.com>
Date: Sun, 5 Nov 2017 01:43:06 +0000 (-0700)
Subject: kaiser: kaiser_flush_tlb_on_return_to_user() check PCID
X-Git-Tag: v3.2.98~7
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bba226006469ef51f310f21b4ef0c6ec833bb98b;p=thirdparty%2Fkernel%2Fstable.git

kaiser: kaiser_flush_tlb_on_return_to_user() check PCID

Let kaiser_flush_tlb_on_return_to_user() do the X86_FEATURE_PCID
check, instead of each caller doing it inline first: nobody needs
to optimize for the noPCID case, it's clearer this way, and better
suits later changes.  Replace those no-op X86_CR3_PCID_KERN_FLUSH lines
by a BUILD_BUG_ON() in load_new_mm_cr3(), in case something changes.

(cherry picked from Change-Id: I9b528ed9d7c1ae4a3b4738c2894ee1740b6fb0b9)

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 63a101f3379ce..88d849e51d724 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -90,7 +90,7 @@ static inline void __native_flush_tlb(void)
 	 * back:
 	 */
 	preempt_disable();
-	if (kaiser_enabled && this_cpu_has(X86_FEATURE_PCID))
+	if (kaiser_enabled)
 		kaiser_flush_tlb_on_return_to_user();
 	native_write_cr3(native_read_cr3());
 	preempt_enable();
@@ -145,7 +145,7 @@ static inline void __native_flush_tlb_single(unsigned long addr)
 	 */
 
 	if (!this_cpu_has(X86_FEATURE_INVPCID_SINGLE)) {
-		if (kaiser_enabled && this_cpu_has(X86_FEATURE_PCID))
+		if (kaiser_enabled)
 			kaiser_flush_tlb_on_return_to_user();
 		asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
 		return;
diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
index 5033206881a79..1e1bed6688489 100644
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -432,12 +432,12 @@ void kaiser_setup_pcid(void)
 
 /*
  * Make a note that this cpu will need to flush USER tlb on return to user.
- * Caller checks whether this_cpu_has(X86_FEATURE_PCID) before calling:
- * if cpu does not, then the NOFLUSH bit will never have been set.
+ * If cpu does not have PCID, then the NOFLUSH bit will never have been set.
  */
 void kaiser_flush_tlb_on_return_to_user(void)
 {
-	this_cpu_write(x86_cr3_pcid_user,
+	if (this_cpu_has(X86_FEATURE_PCID))
+		this_cpu_write(x86_cr3_pcid_user,
 			X86_CR3_PCID_USER_FLUSH | KAISER_SHADOW_PGD_OFFSET);
 }
 EXPORT_SYMBOL(kaiser_flush_tlb_on_return_to_user);
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index ebfae14eb40d5..5e1536b47589c 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -21,7 +21,7 @@ static void load_new_mm_cr3(pgd_t *pgdir)
 {
 	unsigned long new_mm_cr3 = __pa(pgdir);
 
-	if (kaiser_enabled && this_cpu_has(X86_FEATURE_PCID)) {
+	if (kaiser_enabled) {
 		/*
 		 * We reuse the same PCID for different tasks, so we must
 		 * flush all the entries for the PCID out when we change tasks.
@@ -32,10 +32,10 @@ static void load_new_mm_cr3(pgd_t *pgdir)
 		 * do it here, but can only be used if X86_FEATURE_INVPCID is
 		 * available - and many machines support pcid without invpcid.
 		 *
-		 * The line below is a no-op: X86_CR3_PCID_KERN_FLUSH is now 0;
-		 * but keep that line in there in case something changes.
+		 * If X86_CR3_PCID_KERN_FLUSH actually added something, then it
+		 * would be needed in the write_cr3() below - if PCIDs enabled.
 		 */
-		new_mm_cr3 |= X86_CR3_PCID_KERN_FLUSH;
+		BUILD_BUG_ON(X86_CR3_PCID_KERN_FLUSH);
 		kaiser_flush_tlb_on_return_to_user();
 	}