diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2017-12-04 15:07:59 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-12-23 21:13:00 +0100 |
| commit | 6fd166aae78c0ab738d49bda653cbd9e3b1491cf (patch) | |
| tree | ffb632206c0c63c8b83d771097aac3e6b788374a /arch/x86/entry/entry_64.S | |
| parent | 48e111982cda033fec832c6b0592c2acedd85d04 (diff) | |
x86/mm: Use/Fix PCID to optimize user/kernel switches
We can use PCID to retain the TLBs across CR3 switches; including those now
part of the user/kernel switch. This increases performance of kernel
entry/exit at the cost of more expensive/complicated TLB flushing.
Now that we have two address spaces, one for kernel and one for user space,
we need two PCIDs per mm. We use the top PCID bit to indicate a user PCID
(just like we use the PFN LSB for the PGD). Since we do TLB invalidation
from kernel space, the existing code will only invalidate the kernel PCID,
we augment that by marking the corresponding user PCID invalid, and upon
switching back to userspace, use a flushing CR3 write for the switch.
In order to access the user_pcid_flush_mask we use PER_CPU storage, which
means the previously established SWAPGS vs CR3 ordering is now mandatory
and required.
Having to do this memory access does require additional registers, most
sites have a functioning stack and we can spill one (RAX), sites without
functional stack need to otherwise provide the second scratch register.
Note: PCID is generally available on Intel Sandybridge and later CPUs.
Note: Up until this point TLB flushing was broken in this series.
Based-on-code-from: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry/entry_64.S')
| -rw-r--r-- | arch/x86/entry/entry_64.S | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 2ad7ad4d3dd6..fd501844af1f 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -23,7 +23,6 @@ #include <asm/segment.h> #include <asm/cache.h> #include <asm/errno.h> -#include "calling.h" #include <asm/asm-offsets.h> #include <asm/msr.h> #include <asm/unistd.h> @@ -40,6 +39,8 @@ #include <asm/frame.h> #include <linux/err.h> +#include "calling.h" + .code64 .section .entry.text, "ax" @@ -406,7 +407,7 @@ syscall_return_via_sysret: * We are on the trampoline stack. All regs except RDI are live. * We can do future final exit work right here. */ - SWITCH_TO_USER_CR3 scratch_reg=%rdi + SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi popq %rdi popq %rsp @@ -744,7 +745,7 @@ GLOBAL(swapgs_restore_regs_and_return_to_usermode) * We can do future final exit work right here. */ - SWITCH_TO_USER_CR3 scratch_reg=%rdi + SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi /* Restore RDI. */ popq %rdi @@ -857,7 +858,7 @@ native_irq_return_ldt: */ orq PER_CPU_VAR(espfix_stack), %rax - SWITCH_TO_USER_CR3 scratch_reg=%rdi /* to user CR3 */ + SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi SWAPGS /* to user GS */ popq %rdi /* Restore user RDI */ |