From: Alexandre Chartre <alexandre.chartre@oracle.com>
To: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Joel Fernandes <joel@joelfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Juergen Gross <jgross@suse.com>, Brian Gerst <brgerst@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 5 02/31] x86/entry: Provide helpers for execute on irqstack
Date: Mon, 11 May 2020 11:07:43 +0200 [thread overview]
Message-ID: <7477e59e-50d9-3446-dce7-3aa07e74cf5f@oracle.com> (raw)
In-Reply-To: <20200505135828.316937774@linutronix.de>
On 5/5/20 3:53 PM, Thomas Gleixner wrote:
> Device interrupt handlers and system vector handlers are executed on the
> interrupt stack. The stack switch happens in the low level assembly entry
> code. This conflicts with the efforts to consolidate the exit code in C to
> ensure correctness vs. RCU and tracing.
>
> As there is no way to move #DB away from IST due to the MOV SS issue, the
> requirements vs. #DB and NMI for switching to the interrupt stack do not
> exist anymore. The only requirement is that interrupts are disabled.
>
> That allows to move the stack switching to C code which simplifies the
> entry/exit handling further because it allows to switch stacks after
> handling the entry and on exit before handling RCU, return to usermode and
> kernel preemption in the same way as for regular exceptions.
>
> That also allows to move the xen hypercall extra magic code and the softirq
> stack switching into C.
>
> The mechanism is straight forward:
>
> 1) Store the current stack pointer on top of the interrupt stack. That's
> required for the unwinder.
>
> 2) Switch the stack pointer
>
> 3) Call the function
>
> 4) Restore the stackpointer
>
> The full code sequence to make the unwinder happy is:
>
> pushq %rbp
> movq %rsp, %rbp
> movq $(top_of_hardirq_stack - 8), %reg
> movq %rsp, (%reg)
> movq %reg , %rsp
> call function
> popq %rsp
> leaveq
>
> While the following sequence would spare the 'popq %rsp':
>
> pushq %rbp
> movq $(top_of_hardirq_stack - 8), %rbp
> movq %rsp, (%rrbp)
Should be (%rbp) instead of (%rrbp).
> xchgq %rbp, %rsp
> call function
> movq %rbp, %rsp
> leaveq
>
> but that requires further changes to objtool so that the unwinder works
> correctly. Can be done on top and is not critical for now.
>
> Provide helper functions to check whether the interrupt stack is already
> active and whether stack switching is required.
>
> 64 bit only for now. 32 bit has a variant of that already. Once this is
> cleaned up the two implementations might be consolidated as a cleanup on
> top.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/include/asm/irq_stack.h | 61 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 61 insertions(+)
>
> --- /dev/null
> +++ b/arch/x86/include/asm/irq_stack.h
...
> +/*
> + * Macro to emit code for running @func on the irq stack.
> + */
> +#define RUN_ON_IRQSTACK(func) { \
> + unsigned long tos; \
> + \
> + lockdep_assert_irqs_disabled(); \
> + \
> + tos = ((unsigned long)__this_cpu_read(hardirq_stack_ptr)) - 8; \
> + \
> + __this_cpu_add(irq_count, 1); \
> + asm volatile( \
> + "pushq %%rbp \n" \
> + "movq %%rsp, %%rbp \n" \
> + "movq %%rsp, (%[ts]) \n" \
> + "movq %[ts], %%rsp \n" \
> + "1: \n" \
> + " .pushsection .discard.instr_begin \n" \
> + " .long 1b - . \n" \
> + " .popsection \n" \
> + "call " __ASM_FORM(func) " \n" \
> + "2: \n" \
> + " .pushsection .discard.instr_end \n" \
> + " .long 2b - . \n" \
> + " .popsection \n" \
> + "popq %%rsp \n" \
> + "leaveq \n" \
> + : \
> + : [ts] "r" (tos) \
> + : "memory" \
> + ); \
> + __this_cpu_sub(irq_count, 1); \
> +}
The pushsection/popsection discard.instr_begin/end sequences are used several
times in asm() statement at different places, so I wonder if it might be worth
having a macro.
In part 1, patch 20/36 adds instr_begin()/end(): they provide the sequence
but already encapsulated into an asm() statement, then we could do something
like this:
/* Begin/end of an instrumentation safe region */
#define instr_begin_insn(label) \
__stringify(label) ":\n\t" \
".pushsection .discard.instr_begin\n\t" \
".long " __stringify(label) "b - .\n\t" \
".popsection\n\t"
#define instr_end_insn(label) \
__stringify(label) ":\n\t" \
".pushsection .discard.instr_end\n\t" \
".long " __stringify(label) "b - .\n\t" \
".popsection\n\t"
#define instr_begin() ({asm volatile(instr_begin_insn(__COUNTER__));})
#define instr_end() ({asm volatile(instr_end_insn(__COUNTER__));})> +#else /* CONFIG_X86_64 */
And the RUN_ON_IRQSTACK macro would become:
#define RUN_ON_IRQSTACK(func) { \
unsigned long tos; \
\
lockdep_assert_irqs_disabled(); \
\
tos = ((unsigned long)__this_cpu_read(hardirq_stack_ptr)) - 8; \
\
__this_cpu_add(irq_count, 1); \
asm volatile( \
"pushq %%rbp \n" \
"movq %%rsp, %%rbp \n" \
"movq %%rsp, (%[ts]) \n" \
"movq %[ts], %%rsp \n" \
instr_begin_insn(1) \
"call " __ASM_FORM(func) " \n" \
instr_end_insn(2) \
"popq %%rsp \n" \
"leaveq \n" \
: \
: [ts] "r" (tos) \
: "memory" \
); \
__this_cpu_sub(irq_count, 1); \
}
alex.
next prev parent reply other threads:[~2020-05-11 9:09 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 13:53 [patch V4 part 5 00/31] x86/entry: Entry/exception code rework, Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 01/31] genirq: Provide irq_enter/exit_rcu() Thomas Gleixner
2020-05-15 5:53 ` Andy Lutomirski
2020-05-05 13:53 ` [patch V4 part 5 02/31] x86/entry: Provide helpers for execute on irqstack Thomas Gleixner
2020-05-06 8:20 ` Thomas Gleixner
2020-05-10 4:33 ` Lai Jiangshan
2020-05-11 9:07 ` Alexandre Chartre [this message]
2020-05-11 11:54 ` Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 03/31] x86/entry/64: Move softirq stack switch to C Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 04/31] x86/entry: Split idtentry_enter/exit() Thomas Gleixner
2020-05-11 12:42 ` Alexandre Chartre
2020-05-05 13:53 ` [patch V4 part 5 05/31] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY Thomas Gleixner
2020-05-07 2:11 ` Boris Ostrovsky
2020-05-07 8:30 ` Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 06/31] x86/entry/64: Simplify idtentry_body Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 07/31] x86/entry: Provide idtentry_entry/exit_cond_rcu() Thomas Gleixner
2020-05-11 13:53 ` Alexandre Chartre
2020-05-11 14:13 ` Peter Zijlstra
2020-05-12 16:30 ` Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 08/31] x86/entry: Switch page fault exception to IDTENTRY_RAW Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 09/31] x86/entry: Remove the transition leftovers Thomas Gleixner
2020-05-11 14:11 ` Alexandre Chartre
2020-05-05 13:53 ` [patch V4 part 5 10/31] x86/entry: Change exit path of xen_failsafe_callback Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 11/31] x86/entry/64: Remove error_exit Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 12/31] x86/entry/32: Remove common_exception Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 13/31] x86/irq: Convey vector as argument and not in ptregs Thomas Gleixner
2020-05-10 2:44 ` Lai Jiangshan
2020-05-11 14:35 ` Thomas Gleixner
2020-05-11 15:11 ` Lai Jiangshan
2020-05-05 13:53 ` [patch V4 part 5 14/31] x86/irq/64: Provide handle_irq() Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 15/31] x86/entry: Add IRQENTRY_IRQ macro Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 16/31] x86/entry: Use idtentry for interrupts Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 17/31] x86/entry: Provide IDTENTRY_SYSVEC Thomas Gleixner
2020-05-05 13:53 ` [patch V4 part 5 18/31] x86/entry: Convert APIC interrupts to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 19/31] x86/entry: Convert SMP system vectors " Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 20/31] x86/entry: Convert various system vectors Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 21/31] x86/entry: Convert KVM vectors to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 22/31] x86/entry: Convert various hypervisor " Thomas Gleixner
2020-05-06 16:56 ` Wei Liu
2020-05-06 17:11 ` Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 23/31] x86/entry: Convert XEN hypercall vector " Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 24/31] x86/entry: Convert reschedule interrupt to IDTENTRY_RAW Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 25/31] x86/entry: Remove the apic/BUILD interrupt leftovers Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 26/31] x86/entry/64: Remove IRQ stack switching ASM Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 27/31] x86/entry: Make enter_from_user_mode() static Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 28/31] x86/entry/32: Remove redundant irq disable code Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 29/31] x86/entry/64: Remove TRACE_IRQS_*_DEBUG Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 30/31] x86/entry: Move paranoid irq tracing out of ASM code Thomas Gleixner
2020-05-05 13:54 ` [patch V4 part 5 31/31] x86/entry: Remove the TRACE_IRQS cruft Thomas Gleixner
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