linux-kernel - Re: [RFC v3 08/19] arch: um: add shim to trap to allow installing a fault catcher for tests

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Date:   Thu, 29 Nov 2018 19:34:29 -0800
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Brendan Higgins <brendanhiggins@...gle.com>
Cc:     gregkh@...uxfoundation.org, keescook@...gle.com, shuah@...nel.org,
        joel@....id.au, mpe@...erman.id.au, joe@...ches.com, brakmo@...com,
        rostedt@...dmis.org, Tim.Bird@...y.com, khilman@...libre.com,
        julia.lawall@...6.fr, linux-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        jdike@...toit.com, richard@....at, linux-um@...ts.infradead.org,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org, robh@...nel.org,
        dan.j.williams@...el.com, linux-nvdimm@...ts.01.org,
        kieran.bingham@...asonboard.com, frowand.list@...il.com,
        knut.omang@...cle.com
Subject: Re: [RFC v3 08/19] arch: um: add shim to trap to allow installing a
 fault catcher for tests

On Wed, Nov 28, 2018 at 11:36:25AM -0800, Brendan Higgins wrote:
> diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
> index cced829460427..bf90e678b3d71 100644
> --- a/arch/um/kernel/trap.c
> +++ b/arch/um/kernel/trap.c
> @@ -201,6 +201,12 @@ void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
>  	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
>  }
>  
> +static void segv_run_catcher(jmp_buf *catcher, void *fault_addr)
> +{
> +	current->thread.fault_addr = fault_addr;
> +	UML_LONGJMP(catcher, 1);
> +}
> +
>  /*
>   * We give a *copy* of the faultinfo in the regs to segv.
>   * This must be done, since nesting SEGVs could overwrite
> @@ -219,7 +225,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
>  	if (!is_user && regs)
>  		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
>  
> -	if (!is_user && (address >= start_vm) && (address < end_vm)) {
> +	catcher = current->thread.fault_catcher;

This and..

> +	if (catcher && current->thread.is_running_test)
> +		segv_run_catcher(catcher, (void *) address);
> +	else if (!is_user && (address >= start_vm) && (address < end_vm)) {
>  		flush_tlb_kernel_vm();
>  		goto out;
>  	}

*not this*

> @@ -246,12 +255,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
>  		address = 0;
>  	}
>  
> -	catcher = current->thread.fault_catcher;
>  	if (!err)
>  		goto out;
>  	else if (catcher != NULL) {
> -		current->thread.fault_addr = (void *) address;
> -		UML_LONGJMP(catcher, 1);
> +		segv_run_catcher(catcher, (void *) address);
>  	}
>  	else if (current->thread.fault_addr != NULL)
>  		panic("fault_addr set but no fault catcher");

But with this seems one atomic change which should be submitted
separately, its just a helper. Think it would make the actual
change needed easier to review, ie, your needed changes would
be smaller and clearer for what you need.

  Luis