[PATCH 20/23] x86, mm: put mmu-to-h/w ASID translation in one place

[Dave Hansen]

We effectively have two ASID types:
1. The one stored in the mmu_context that goes from 0->5
2. The one we program into the hardware that goes from 1->6

Let's just put the +1 in a single place which gives us a
nice place to comment.  KAISER will also need to, given an
ASID, know which hardware ASID to flush for the userspace
mapping.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Moritz Lipp <moritz.lipp@xxxxxxxxxxxxxx>
Cc: Daniel Gruss <daniel.gruss@xxxxxxxxxxxxxx>
Cc: Michael Schwarz <michael.schwarz@xxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
---

 b/arch/x86/include/asm/tlbflush.h |   30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff -puN arch/x86/include/asm/tlbflush.h~kaiser-pcid-pre-build-kern arch/x86/include/asm/tlbflush.h
--- a/arch/x86/include/asm/tlbflush.h~kaiser-pcid-pre-build-kern	2017-10-31 15:03:59.699555275 -0700
+++ b/arch/x86/include/asm/tlbflush.h	2017-10-31 15:03:59.703555465 -0700
@@ -86,21 +86,26 @@ static inline u64 inc_mm_tlb_gen(struct
  */
 #define NR_AVAIL_ASIDS ((1<<CR3_AVAIL_ASID_BITS) - 1)
 
-/*
- * If PCID is on, ASID-aware code paths put the ASID+1 into the PCID
- * bits.  This serves two purposes.  It prevents a nasty situation in
- * which PCID-unaware code saves CR3, loads some other value (with PCID
- * == 0), and then restores CR3, thus corrupting the TLB for ASID 0 if
- * the saved ASID was nonzero.  It also means that any bugs involving
- * loading a PCID-enabled CR3 with CR4.PCIDE off will trigger
- * deterministically.
- */
+static inline u16 kern_asid(u16 asid)
+{
+	VM_WARN_ON_ONCE(asid >= NR_AVAIL_ASIDS);
+	/*
+	 * If PCID is on, ASID-aware code paths put the ASID+1 into the PCID
+	 * bits.  This serves two purposes.  It prevents a nasty situation in
+	 * which PCID-unaware code saves CR3, loads some other value (with PCID
+	 * == 0), and then restores CR3, thus corrupting the TLB for ASID 0 if
+	 * the saved ASID was nonzero.  It also means that any bugs involving
+	 * loading a PCID-enabled CR3 with CR4.PCIDE off will trigger
+	 * deterministically.
+	 */
+	return asid + 1;
+}
+
 struct pgd_t;
 static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
 {
 	if (static_cpu_has(X86_FEATURE_PCID)) {
-		VM_WARN_ON_ONCE(asid > NR_AVAIL_ASIDS);
-		return __sme_pa(pgd) | (asid + 1);
+		return __sme_pa(pgd) | kern_asid(asid);
 	} else {
 		VM_WARN_ON_ONCE(asid != 0);
 		return __sme_pa(pgd);
@@ -110,7 +115,8 @@ static inline unsigned long build_cr3(pg
 static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
 {
 	VM_WARN_ON_ONCE(asid > NR_AVAIL_ASIDS);
-	return __sme_pa(pgd) | (asid + 1) | CR3_NOFLUSH;
+	VM_WARN_ON_ONCE(!this_cpu_has(X86_FEATURE_PCID));
+	return __sme_pa(pgd) | kern_asid(asid) | CR3_NOFLUSH;
 }
 
 #ifdef CONFIG_PARAVIRT
_