From: Mark Rutland <mark.rutland@arm.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: keescook@chromium.org, maz@kernel.org, robin.murphy@arm.com,
broonie@kernel.org, james.morse@arm.com,
julien.thierry.kdev@gmail.com, catalin.marinas@arm.com,
labbott@redhat.com, will@kernel.org,
linux-arm-kernel@lists.infradead.org, alex.popov@linux.com
Subject: Re: [PATCH 12/17] arm64: debug-monitors: refactor MDSCR manipulation
Date: Fri, 10 Jan 2020 16:09:41 +0000 [thread overview]
Message-ID: <20200110160941.GH33536@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <c616e5c0-301c-7c26-6954-9e287e6c9673@arm.com>
On Fri, Jan 10, 2020 at 10:05:48AM +0530, Anshuman Khandual wrote:
>
>
> On 01/09/2020 12:26 AM, Mark Rutland wrote:
> > When we convert the ret_to_user/work_pending code to C, we're going to
> > want to poke the MDSCR to enable/disable single-step. Let's factor out
> > the existing code for this from debug-monitors.c.
> >
> > At the same time, we can make use of {read,write}_sysreg() directly, and
> > get rid of the mdscr_{read,write} wrappers.
> >
> > The existing code masked DAIF when manipulating MDSCR_EL1, but this
> > should not be necessary. Exceptions can be taken immediately before DAIF
> > is masked, and given the lack of an ISB can also be taken after DAIF is
> > unmasked as writes to DAIF are only self-synchronizing and not
> > context-synchronizing in general. We may want to add an ISB to ensure
> > that updates to MDSCR have taken effect, however.
>
> Any reason this patch choose not add that ISB for now after writing
> mdscr_el1 register via sysreg_clear_set().
I didn't want to make that functional change without justification. For
example, the ISB wouldn't be needed for changes that only affect
userspace.
Thanks,
Mark.
>
> >
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > ---
> > arch/arm64/include/asm/debug-monitors.h | 10 ++++++++++
> > arch/arm64/kernel/debug-monitors.c | 32 +++++++-------------------------
> > 2 files changed, 17 insertions(+), 25 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/debug-monitors.h b/arch/arm64/include/asm/debug-monitors.h
> > index 7619f473155f..342867e50c54 100644
> > --- a/arch/arm64/include/asm/debug-monitors.h
> > +++ b/arch/arm64/include/asm/debug-monitors.h
> > @@ -107,6 +107,16 @@ enum dbg_active_el {
> > void enable_debug_monitors(enum dbg_active_el el);
> > void disable_debug_monitors(enum dbg_active_el el);
> >
> > +static __always_inline void __enable_single_step_nosync(void)
> > +{
> > + sysreg_clear_set(mdscr_el1, 0, DBG_MDSCR_SS);
> > +}
> > +
> > +static __always_inline void __disable_single_step_nosync(void)
> > +{
> > + sysreg_clear_set(mdscr_el1, DBG_MDSCR_SS, 0);
> > +}
> > +
> > void user_rewind_single_step(struct task_struct *task);
> > void user_fastforward_single_step(struct task_struct *task);
> >
> > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> > index 48222a4760c2..fa2d4145bd07 100644
> > --- a/arch/arm64/kernel/debug-monitors.c
> > +++ b/arch/arm64/kernel/debug-monitors.c
> > @@ -32,24 +32,6 @@ u8 debug_monitors_arch(void)
> > }
> >
> > /*
> > - * MDSCR access routines.
> > - */
> > -static void mdscr_write(u32 mdscr)
> > -{
> > - unsigned long flags;
> > - flags = local_daif_save();
> > - write_sysreg(mdscr, mdscr_el1);
> > - local_daif_restore(flags);
> > -}
> > -NOKPROBE_SYMBOL(mdscr_write);
> > -
> > -static u32 mdscr_read(void)
> > -{
> > - return read_sysreg(mdscr_el1);
> > -}
> > -NOKPROBE_SYMBOL(mdscr_read);
> > -
> > -/*
> > * Allow root to disable self-hosted debug from userspace.
> > * This is useful if you want to connect an external JTAG debugger.
> > */
> > @@ -91,9 +73,9 @@ void enable_debug_monitors(enum dbg_active_el el)
> > enable |= DBG_MDSCR_KDE;
> >
> > if (enable && debug_enabled) {
> > - mdscr = mdscr_read();
> > + mdscr = read_sysreg(mdscr_el1);
> > mdscr |= enable;
> > - mdscr_write(mdscr);
> > + write_sysreg(mdscr, mdscr_el1);
> > }
> > }
> > NOKPROBE_SYMBOL(enable_debug_monitors);
> > @@ -112,9 +94,9 @@ void disable_debug_monitors(enum dbg_active_el el)
> > disable &= ~DBG_MDSCR_KDE;
> >
> > if (disable) {
> > - mdscr = mdscr_read();
> > + mdscr = read_sysreg(mdscr_el1);
> > mdscr &= disable;
> > - mdscr_write(mdscr);
> > + write_sysreg(mdscr, mdscr_el1);
> > }
> > }
> > NOKPROBE_SYMBOL(disable_debug_monitors);
> > @@ -409,7 +391,7 @@ void kernel_enable_single_step(struct pt_regs *regs)
> > {
> > WARN_ON(!irqs_disabled());
> > set_regs_spsr_ss(regs);
> > - mdscr_write(mdscr_read() | DBG_MDSCR_SS);
> > + __enable_single_step_nosync();
> > enable_debug_monitors(DBG_ACTIVE_EL1);
> > }
> > NOKPROBE_SYMBOL(kernel_enable_single_step);
> > @@ -417,7 +399,7 @@ NOKPROBE_SYMBOL(kernel_enable_single_step);
> > void kernel_disable_single_step(void)
> > {
> > WARN_ON(!irqs_disabled());
> > - mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
> > + __disable_single_step_nosync();
> > disable_debug_monitors(DBG_ACTIVE_EL1);
> > }
> > NOKPROBE_SYMBOL(kernel_disable_single_step);
> > @@ -425,7 +407,7 @@ NOKPROBE_SYMBOL(kernel_disable_single_step);
> > int kernel_active_single_step(void)
> > {
> > WARN_ON(!irqs_disabled());
> > - return mdscr_read() & DBG_MDSCR_SS;
> > + return read_sysreg(mdscr_el1) & DBG_MDSCR_SS;
> > }
> > NOKPROBE_SYMBOL(kernel_active_single_step);
> >
> >
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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next prev parent reply other threads:[~2020-01-10 16:09 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-08 18:56 [PATCH 00/17] arm64: entry deasmification and cleanup Mark Rutland
2020-01-08 18:56 ` [PATCH 01/17] arm64: entry: mark all entry code as notrace Mark Rutland
2020-01-09 5:21 ` Anshuman Khandual
2020-01-13 15:44 ` Mark Rutland
2020-01-08 18:56 ` [PATCH 02/17] arm64: entry: cleanup el0 svc handler naming Mark Rutland
2020-01-09 5:33 ` Anshuman Khandual
2020-01-08 18:56 ` [PATCH 03/17] arm64: entry: move arm64_preempt_schedule_irq to entry-common.c Mark Rutland
2020-01-09 5:36 ` Anshuman Khandual
2020-01-08 18:56 ` [PATCH 04/17] arm64: entry: move preempt logic to C Mark Rutland
2020-01-09 6:43 ` Anshuman Khandual
2020-01-09 12:22 ` Mark Rutland
2020-01-08 18:56 ` [PATCH 05/17] arm64: entry: add a call_on_stack helper Mark Rutland
2020-01-09 8:00 ` Anshuman Khandual
2020-01-14 18:24 ` Mark Rutland
2020-01-09 14:30 ` Laura Abbott
2020-01-09 14:46 ` Mark Rutland
2020-01-08 18:56 ` [PATCH 06/17] arm64: entry: convert irq entry to C Mark Rutland
2020-01-08 18:56 ` [PATCH 07/17] arm64: entry: convert error " Mark Rutland
2020-01-09 9:12 ` Anshuman Khandual
2020-01-09 12:49 ` Mark Rutland
2020-01-08 18:56 ` [PATCH 08/17] arm64: entry: Split el0_sync_compat from el0_sync Mark Rutland
2020-01-09 9:50 ` Anshuman Khandual
2020-01-08 18:56 ` [PATCH 09/17] arm64: entry: organise handler stubs consistently Mark Rutland
2020-01-09 10:01 ` Anshuman Khandual
2020-01-08 18:56 ` [PATCH 10/17] arm64: entry: consolidate EL1 return paths Mark Rutland
2020-01-10 3:39 ` Anshuman Khandual
2020-01-10 16:02 ` Mark Rutland
2020-01-08 18:56 ` [PATCH 11/17] stackleak: allow C to call stackleak_erase() Mark Rutland
2020-01-10 3:45 ` Anshuman Khandual
2020-01-10 16:07 ` Mark Rutland
2020-01-27 23:00 ` Kees Cook
2020-01-08 18:56 ` [PATCH 12/17] arm64: debug-monitors: refactor MDSCR manipulation Mark Rutland
2020-01-10 4:35 ` Anshuman Khandual
2020-01-10 16:09 ` Mark Rutland [this message]
2020-01-08 18:56 ` [PATCH 13/17] arm64: entry: move common el0 entry/return work to C Mark Rutland
2020-01-09 15:19 ` Mark Rutland
2020-01-08 18:56 ` [PATCH 14/17] arm64: entry: move NO_SYSCALL setup " Mark Rutland
2020-01-10 5:37 ` Anshuman Khandual
2020-01-08 18:56 ` [PATCH 15/17] arm64: entry: move ARM64_ERRATUM_845719 workaround " Mark Rutland
2020-01-08 18:56 ` [PATCH 16/17] arm64: entry: move ARM64_ERRATUM_1418040 " Mark Rutland
2020-01-08 18:56 ` [PATCH 17/17] arm64: entry: cleanup sp_el0 manipulation Mark Rutland
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