linux-kernel - Re: [PATCH 10/18] arm64: convert native/compat syscall entry to C

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Message-ID: <20180514115805.bdlcxsw6q3xsbjb7@lakrids.cambridge.arm.com>
Date:   Mon, 14 May 2018 12:58:05 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Dave Martin <Dave.Martin@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, marc.zyngier@....com,
        catalin.marinas@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, linux@...inikbrodowski.net,
        james.morse@....com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 10/18] arm64: convert native/compat syscall entry to C

On Mon, May 14, 2018 at 12:07:30PM +0100, Dave Martin wrote:
> On Mon, May 14, 2018 at 10:46:32AM +0100, Mark Rutland wrote:

> > diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
> > index 5df857e32b48..4706f841e758 100644
> > --- a/arch/arm64/kernel/syscall.c
> > +++ b/arch/arm64/kernel/syscall.c
> > @@ -6,7 +6,9 @@
> >  #include <linux/ptrace.h>
> >  
> >  #include <asm/daifflags.h>
> > +#include <asm/fpsimd.h>
> >  #include <asm/thread_info.h>
> > +#include <asm/unistd.h>
> >  
> >  long do_ni_syscall(struct pt_regs *regs);
> >  
> > @@ -41,8 +43,8 @@ static inline bool has_syscall_work(unsigned long flags)
> >  int syscall_trace_enter(struct pt_regs *regs);
> >  void syscall_trace_exit(struct pt_regs *regs);
> >  
> > -asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
> > -			       syscall_fn_t syscall_table[])
> > +static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
> > +			   syscall_fn_t syscall_table[])
> >  {
> >  	unsigned long flags = current_thread_info()->flags;
> >  
> > @@ -79,3 +81,37 @@ asmlinkage void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
> >  trace_exit:
> >  	syscall_trace_exit(regs);
> >  }
> > +
> > +static inline void sve_user_reset(void)
> 
> Static function with no caller...

Ugh, this was intended to be called below in el0_svc_handler().

> > +{
> > +	if (!system_supports_sve())
> > +		return;
> > +
> > +	/*
> > +	 * task_fpsimd_load() won't be called to update CPACR_EL1 in
> > +	 * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
> > +	 * happens if a context switch or kernel_neon_begin() or context
> > +	 * modification (sigreturn, ptrace) intervenes.
> > +	 * So, ensure that CPACR_EL1 is already correct for the fast-path case.
> > +	 */
> > +	if (test_and_clear_thread_flag(TIF_SVE))
> > +		sve_user_disable();
> 
> sve_user_disable() is already inline, and incorporates the if()
> internally via sysreg_clear_set().
> 
> So, should this just be
> 
> 	clear_thread_flag(TIF_SVE);
> 	sve_user_disable();

Sure. That does mean we'll unconditionally read cpacr_el1, but I assume
you're happy with that. I'll note the difference in the commit message.

> > +}
> > +
> > +extern syscall_fn_t sys_call_table[];
> > +
> > +asmlinkage void el0_svc_handler(struct pt_regs *regs)
> > +{
> 
> if (system_supports_sve()) ?
> 
> > +	sve_user_disable();
> 
> Or should this be replaced by a call to sve_user_reset()?
> 
> I suspect the latter, since we do want to be clearing TIF_SVE here too.

Yes, this was mean to be sve_user_reset().

Thanks,
Mark.