From 0a126abd576ebc6403f063dbe20cf7416c9d9393 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 5 Dec 2017 13:34:53 +0100 Subject: [PATCH] x86/mm: Clarify the whole ASID/kernel PCID/user PCID naming Ideally we'd also use sparse to enforce this separation so it becomes much more difficult to mess up. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Cc: Andy Lutomirski Cc: Boris Ostrovsky Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: David Laight Cc: Denys Vlasenko Cc: Eduardo Valentin Cc: Greg KH Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Will Deacon Cc: aliguori@amazon.com Cc: daniel.gruss@iaik.tugraz.at Cc: hughd@google.com Cc: keescook@google.com Cc: linux-mm@kvack.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/tlbflush.h | 55 ++++++++++++++++++++++++++------- 1 file changed, 43 insertions(+), 12 deletions(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index 57072a1052fe..b519da4fc03c 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -13,16 +13,33 @@ #include #include -static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) -{ - /* - * Bump the generation count. This also serves as a full barrier - * that synchronizes with switch_mm(): callers are required to order - * their read of mm_cpumask after their writes to the paging - * structures. - */ - return atomic64_inc_return(&mm->context.tlb_gen); -} +/* + * The x86 feature is called PCID (Process Context IDentifier). It is similar + * to what is traditionally called ASID on the RISC processors. + * + * We don't use the traditional ASID implementation, where each process/mm gets + * its own ASID and flush/restart when we run out of ASID space. + * + * Instead we have a small per-cpu array of ASIDs and cache the last few mm's + * that came by on this CPU, allowing cheaper switch_mm between processes on + * this CPU. + * + * We end up with different spaces for different things. To avoid confusion we + * use different names for each of them: + * + * ASID - [0, TLB_NR_DYN_ASIDS-1] + * the canonical identifier for an mm + * + * kPCID - [1, TLB_NR_DYN_ASIDS] + * the value we write into the PCID part of CR3; corresponds to the + * ASID+1, because PCID 0 is special. + * + * uPCID - [2048 + 1, 2048 + TLB_NR_DYN_ASIDS] + * for KPTI each mm has two address spaces and thus needs two + * PCID values, but we can still do with a single ASID denomination + * for each mm. Corresponds to kPCID + 2048. + * + */ /* There are 12 bits of space for ASIDS in CR3 */ #define CR3_HW_ASID_BITS 12 @@ -41,7 +58,7 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) /* * ASIDs are zero-based: 0->MAX_AVAIL_ASID are valid. -1 below to account - * for them being zero-based. Another -1 is because ASID 0 is reserved for + * for them being zero-based. Another -1 is because PCID 0 is reserved for * use by non-PCID-aware users. */ #define MAX_ASID_AVAILABLE ((1 << CR3_AVAIL_PCID_BITS) - 2) @@ -52,6 +69,9 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) */ #define TLB_NR_DYN_ASIDS 6 +/* + * Given @asid, compute kPCID + */ static inline u16 kern_pcid(u16 asid) { VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE); @@ -86,7 +106,7 @@ static inline u16 kern_pcid(u16 asid) } /* - * The user PCID is just the kernel one, plus the "switch bit". + * Given @asid, compute uPCID */ static inline u16 user_pcid(u16 asid) { @@ -484,6 +504,17 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a) void native_flush_tlb_others(const struct cpumask *cpumask, const struct flush_tlb_info *info); +static inline u64 inc_mm_tlb_gen(struct mm_struct *mm) +{ + /* + * Bump the generation count. This also serves as a full barrier + * that synchronizes with switch_mm(): callers are required to order + * their read of mm_cpumask after their writes to the paging + * structures. + */ + return atomic64_inc_return(&mm->context.tlb_gen); +} + static inline void arch_tlbbatch_add_mm(struct arch_tlbflush_unmap_batch *batch, struct mm_struct *mm) { -- 2.30.2