* [PATCH 0/2] x86/entry: Trade cycles
@ 2023-11-20 14:33 Peter Zijlstra
2023-11-20 14:33 ` [PATCH 1/2] x86/entry: Optimize common_interrupt_return() Peter Zijlstra
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Peter Zijlstra @ 2023-11-20 14:33 UTC (permalink / raw)
To: x86; +Cc: linux-kernel, peterz
Hi,
Two little patches that trade a little performance. First patch optimizes
(although I couldn't get definite numbers showing it makes a difference) the
return to user path by avoiding some PTI specifics in the generic path.
Second patch then steals some of the won cycles by making a debug check
unconditional.
This came forth from a discussion with amluto who lamented we only had the
debug check conditional on DEBUG_ENTRY.
^ permalink raw reply [flat|nested] 6+ messages in thread* [PATCH 1/2] x86/entry: Optimize common_interrupt_return() 2023-11-20 14:33 [PATCH 0/2] x86/entry: Trade cycles Peter Zijlstra @ 2023-11-20 14:33 ` Peter Zijlstra 2023-11-21 13:04 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra 2023-11-20 14:33 ` [PATCH 2/2] x86/entry: Harden return-to-user Peter Zijlstra 2023-11-21 15:26 ` [PATCH 0/2] x86/entry: Trade cycles Thomas Gleixner 2 siblings, 1 reply; 6+ messages in thread From: Peter Zijlstra @ 2023-11-20 14:33 UTC (permalink / raw) To: x86; +Cc: linux-kernel, peterz The code in common_interrupt_return() does a bunch of unconditional work that is really only needed on PTI kernels. Specifically it unconditionally copies the IRET frame back onto the entry stack, swizzles onto the entry stack and does IRET from there. However, without PTI we can simply IRET from whatever stack we're on. ivb-ep, mitigations=off, gettid-1m: PRE: 140,118,538 cycles:k ( +- 0.01% ) 236,692,878 instructions:k # 1.69 insn per cycle ( +- 0.00% ) POST: 140,026,608 cycles:k ( +- 0.01% ) 236,696,176 instructions:k # 1.69 insn per cycle ( +- 0.00% ) (this is with --repeat 100 and the run-to-run variance is bigger than the difference shown) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/entry/calling.h | 12 +++++++++--- arch/x86/entry/entry_64.S | 17 +++++++++++++++-- 2 files changed, 24 insertions(+), 5 deletions(-) --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -175,8 +175,7 @@ For 32-bit we have the following convent #define THIS_CPU_user_pcid_flush_mask \ PER_CPU_VAR(cpu_tlbstate + TLB_STATE_user_pcid_flush_mask) -.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req - ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI +.macro SWITCH_TO_USER_CR3 scratch_reg:req scratch_reg2:req mov %cr3, \scratch_reg ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID @@ -206,13 +205,20 @@ For 32-bit we have the following convent /* Flip the PGD to the user version */ orq $(PTI_USER_PGTABLE_MASK), \scratch_reg mov \scratch_reg, %cr3 +.endm + +.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req + ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI + SWITCH_TO_USER_CR3 \scratch_reg \scratch_reg2 .Lend_\@: .endm .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req + ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI pushq %rax - SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax + SWITCH_TO_USER_CR3 scratch_reg=\scratch_reg scratch_reg2=%rax popq %rax +.Lend_\@: .endm .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -569,7 +569,18 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_ #ifdef CONFIG_XEN_PV ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV #endif +#ifdef CONFIG_PAGE_TABLE_ISOLATION + ALTERNATIVE "", "jmp .Lpti_restore_regs_and_return_to_usermode", X86_FEATURE_PTI +#endif + + STACKLEAK_ERASE + POP_REGS + add $8, %rsp /* orig_ax */ + swapgs + jmp .Lnative_iret +#ifdef CONFIG_PAGE_TABLE_ISOLATION +.Lpti_restore_regs_and_return_to_usermode: POP_REGS pop_rdi=0 /* @@ -596,13 +607,15 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_ */ STACKLEAK_ERASE_NOCLOBBER - SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi + push %rax + SWITCH_TO_USER_CR3 scratch_reg=%rdi scratch_reg2=%rax + pop %rax /* Restore RDI. */ popq %rdi swapgs jmp .Lnative_iret - +#endif SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL) #ifdef CONFIG_DEBUG_ENTRY ^ permalink raw reply [flat|nested] 6+ messages in thread
* [tip: x86/entry] x86/entry: Optimize common_interrupt_return() 2023-11-20 14:33 ` [PATCH 1/2] x86/entry: Optimize common_interrupt_return() Peter Zijlstra @ 2023-11-21 13:04 ` tip-bot2 for Peter Zijlstra 0 siblings, 0 replies; 6+ messages in thread From: tip-bot2 for Peter Zijlstra @ 2023-11-21 13:04 UTC (permalink / raw) To: linux-tip-commits Cc: Peter Zijlstra (Intel), Ingo Molnar, Linus Torvalds, x86, linux-kernel The following commit has been merged into the x86/entry branch of tip: Commit-ID: c516213726fb572700cce4a5909aa8d82b77192a Gitweb: https://git.kernel.org/tip/c516213726fb572700cce4a5909aa8d82b77192a Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 20 Nov 2023 15:33:45 +01:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Tue, 21 Nov 2023 13:57:30 +01:00 x86/entry: Optimize common_interrupt_return() The code in common_interrupt_return() does a bunch of unconditional work that is really only needed on PTI kernels. Specifically it unconditionally copies the IRET frame back onto the entry stack, swizzles onto the entry stack and does IRET from there. However, without PTI we can simply IRET from whatever stack we're on. ivb-ep, mitigations=off, gettid-1m: PRE: 140,118,538 cycles:k ( +- 0.01% ) 236,692,878 instructions:k # 1.69 insn per cycle ( +- 0.00% ) POST: 140,026,608 cycles:k ( +- 0.01% ) 236,696,176 instructions:k # 1.69 insn per cycle ( +- 0.00% ) (this is with --repeat 100 and the run-to-run variance is bigger than the difference shown) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20231120143626.638107480@infradead.org --- arch/x86/entry/calling.h | 12 +++++++++--- arch/x86/entry/entry_64.S | 17 +++++++++++++++-- 2 files changed, 24 insertions(+), 5 deletions(-) diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index f690762..9f1d947 100644 --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -175,8 +175,7 @@ For 32-bit we have the following conventions - kernel is built with #define THIS_CPU_user_pcid_flush_mask \ PER_CPU_VAR(cpu_tlbstate) + TLB_STATE_user_pcid_flush_mask -.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req - ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI +.macro SWITCH_TO_USER_CR3 scratch_reg:req scratch_reg2:req mov %cr3, \scratch_reg ALTERNATIVE "jmp .Lwrcr3_\@", "", X86_FEATURE_PCID @@ -206,13 +205,20 @@ For 32-bit we have the following conventions - kernel is built with /* Flip the PGD to the user version */ orq $(PTI_USER_PGTABLE_MASK), \scratch_reg mov \scratch_reg, %cr3 +.endm + +.macro SWITCH_TO_USER_CR3_NOSTACK scratch_reg:req scratch_reg2:req + ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI + SWITCH_TO_USER_CR3 \scratch_reg \scratch_reg2 .Lend_\@: .endm .macro SWITCH_TO_USER_CR3_STACK scratch_reg:req + ALTERNATIVE "jmp .Lend_\@", "", X86_FEATURE_PTI pushq %rax - SWITCH_TO_USER_CR3_NOSTACK scratch_reg=\scratch_reg scratch_reg2=%rax + SWITCH_TO_USER_CR3 scratch_reg=\scratch_reg scratch_reg2=%rax popq %rax +.Lend_\@: .endm .macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index de6469d..dfbf799 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -569,7 +569,18 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) #ifdef CONFIG_XEN_PV ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV #endif +#ifdef CONFIG_PAGE_TABLE_ISOLATION + ALTERNATIVE "", "jmp .Lpti_restore_regs_and_return_to_usermode", X86_FEATURE_PTI +#endif + + STACKLEAK_ERASE + POP_REGS + add $8, %rsp /* orig_ax */ + swapgs + jmp .Lnative_iret +#ifdef CONFIG_PAGE_TABLE_ISOLATION +.Lpti_restore_regs_and_return_to_usermode: POP_REGS pop_rdi=0 /* @@ -596,13 +607,15 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) */ STACKLEAK_ERASE_NOCLOBBER - SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi + push %rax + SWITCH_TO_USER_CR3 scratch_reg=%rdi scratch_reg2=%rax + pop %rax /* Restore RDI. */ popq %rdi swapgs jmp .Lnative_iret - +#endif SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL) #ifdef CONFIG_DEBUG_ENTRY ^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH 2/2] x86/entry: Harden return-to-user 2023-11-20 14:33 [PATCH 0/2] x86/entry: Trade cycles Peter Zijlstra 2023-11-20 14:33 ` [PATCH 1/2] x86/entry: Optimize common_interrupt_return() Peter Zijlstra @ 2023-11-20 14:33 ` Peter Zijlstra 2023-11-21 13:04 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra 2023-11-21 15:26 ` [PATCH 0/2] x86/entry: Trade cycles Thomas Gleixner 2 siblings, 1 reply; 6+ messages in thread From: Peter Zijlstra @ 2023-11-20 14:33 UTC (permalink / raw) To: x86; +Cc: linux-kernel, peterz Make the DEBUG_ENTRY check that validates CS is a user segment unconditional and move it nearer to IRET. PRE: 140,026,608 cycles:k ( +- 0.01% ) 236,696,176 instructions:k # 1.69 insn per cycle ( +- 0.00% ) POST: 139,957,681 cycles:k ( +- 0.01% ) 236,681,819 instructions:k # 1.69 insn per cycle ( +- 0.00% ) (this is with --repeat 100 and the run-to-run variance is bigger than the difference shown) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/entry/entry_64.S | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -559,13 +559,6 @@ SYM_CODE_END(\asmsym) SYM_CODE_START_LOCAL(common_interrupt_return) SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) IBRS_EXIT -#ifdef CONFIG_DEBUG_ENTRY - /* Assert that pt_regs indicates user mode. */ - testb $3, CS(%rsp) - jnz 1f - ud2 -1: -#endif #ifdef CONFIG_XEN_PV ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV #endif @@ -576,8 +569,14 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_ STACKLEAK_ERASE POP_REGS add $8, %rsp /* orig_ax */ + UNWIND_HINT_IRET_REGS + +.Lswapgs_and_iret: swapgs - jmp .Lnative_iret + /* Assert that the IRET frame indicates user mode. */ + testb $3, 8(%rsp) + jnz .Lnative_iret + ud2 #ifdef CONFIG_PAGE_TABLE_ISOLATION .Lpti_restore_regs_and_return_to_usermode: @@ -613,8 +612,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_ /* Restore RDI. */ popq %rdi - swapgs - jmp .Lnative_iret + jmp .Lswapgs_and_iret #endif SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL) ^ permalink raw reply [flat|nested] 6+ messages in thread
* [tip: x86/entry] x86/entry: Harden return-to-user 2023-11-20 14:33 ` [PATCH 2/2] x86/entry: Harden return-to-user Peter Zijlstra @ 2023-11-21 13:04 ` tip-bot2 for Peter Zijlstra 0 siblings, 0 replies; 6+ messages in thread From: tip-bot2 for Peter Zijlstra @ 2023-11-21 13:04 UTC (permalink / raw) To: linux-tip-commits Cc: Peter Zijlstra (Intel), Ingo Molnar, Linus Torvalds, x86, linux-kernel The following commit has been merged into the x86/entry branch of tip: Commit-ID: 1e4d3001f59fb7a9917cb746544b65e616b5f809 Gitweb: https://git.kernel.org/tip/1e4d3001f59fb7a9917cb746544b65e616b5f809 Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Mon, 20 Nov 2023 15:33:46 +01:00 Committer: Ingo Molnar <mingo@kernel.org> CommitterDate: Tue, 21 Nov 2023 13:57:31 +01:00 x86/entry: Harden return-to-user Make the CONFIG_DEBUG_ENTRY=y check that validates CS is a user segment unconditional and move it nearer to IRET. PRE: 140,026,608 cycles:k ( +- 0.01% ) 236,696,176 instructions:k # 1.69 insn per cycle ( +- 0.00% ) POST: 139,957,681 cycles:k ( +- 0.01% ) 236,681,819 instructions:k # 1.69 insn per cycle ( +- 0.00% ) (this is with --repeat 100 and the run-to-run variance is bigger than the difference shown) Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: https://lore.kernel.org/r/20231120143626.753200755@infradead.org --- arch/x86/entry/entry_64.S | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index dfbf799..c40f89a 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -559,13 +559,6 @@ __irqentry_text_end: SYM_CODE_START_LOCAL(common_interrupt_return) SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) IBRS_EXIT -#ifdef CONFIG_DEBUG_ENTRY - /* Assert that pt_regs indicates user mode. */ - testb $3, CS(%rsp) - jnz 1f - ud2 -1: -#endif #ifdef CONFIG_XEN_PV ALTERNATIVE "", "jmp xenpv_restore_regs_and_return_to_usermode", X86_FEATURE_XENPV #endif @@ -576,8 +569,14 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) STACKLEAK_ERASE POP_REGS add $8, %rsp /* orig_ax */ + UNWIND_HINT_IRET_REGS + +.Lswapgs_and_iret: swapgs - jmp .Lnative_iret + /* Assert that the IRET frame indicates user mode. */ + testb $3, 8(%rsp) + jnz .Lnative_iret + ud2 #ifdef CONFIG_PAGE_TABLE_ISOLATION .Lpti_restore_regs_and_return_to_usermode: @@ -613,8 +612,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_return_to_usermode, SYM_L_GLOBAL) /* Restore RDI. */ popq %rdi - swapgs - jmp .Lnative_iret + jmp .Lswapgs_and_iret #endif SYM_INNER_LABEL(restore_regs_and_return_to_kernel, SYM_L_GLOBAL) ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 0/2] x86/entry: Trade cycles 2023-11-20 14:33 [PATCH 0/2] x86/entry: Trade cycles Peter Zijlstra 2023-11-20 14:33 ` [PATCH 1/2] x86/entry: Optimize common_interrupt_return() Peter Zijlstra 2023-11-20 14:33 ` [PATCH 2/2] x86/entry: Harden return-to-user Peter Zijlstra @ 2023-11-21 15:26 ` Thomas Gleixner 2 siblings, 0 replies; 6+ messages in thread From: Thomas Gleixner @ 2023-11-21 15:26 UTC (permalink / raw) To: Peter Zijlstra, x86; +Cc: linux-kernel, peterz On Mon, Nov 20 2023 at 15:33, Peter Zijlstra wrote: > Two little patches that trade a little performance. First patch optimizes > (although I couldn't get definite numbers showing it makes a difference) the > return to user path by avoiding some PTI specifics in the generic path. > > Second patch then steals some of the won cycles by making a debug check > unconditional. > > This came forth from a discussion with amluto who lamented we only had the > debug check conditional on DEBUG_ENTRY. Reviewed-by: Thomas Gleixner <tglx@linutronix.de> ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-11-21 15:26 UTC | newest] Thread overview: 6+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2023-11-20 14:33 [PATCH 0/2] x86/entry: Trade cycles Peter Zijlstra 2023-11-20 14:33 ` [PATCH 1/2] x86/entry: Optimize common_interrupt_return() Peter Zijlstra 2023-11-21 13:04 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra 2023-11-20 14:33 ` [PATCH 2/2] x86/entry: Harden return-to-user Peter Zijlstra 2023-11-21 13:04 ` [tip: x86/entry] " tip-bot2 for Peter Zijlstra 2023-11-21 15:26 ` [PATCH 0/2] x86/entry: Trade cycles Thomas Gleixner
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