Re: [PATCH v5 5/7] xen/riscv: introduce trap_init()

[Julien Grall <julien@xxxxxxx>]

On 22/03/2023 11:33, Oleksii wrote:
> Hi Julien,
Hi Oleksii,

> On Tue, 2023-03-21 at 17:42 +0000, Julien Grall wrote:
> > Hi Oleksii,
> >
> > On 16/03/2023 14:39, Oleksii Kurochko wrote:
> > > Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> > > Reviewed-by: Alistair Francis <alistair.francis@xxxxxxx>
> > > ---
> > > Changes in V5:
> > >     - Nothing changed
> > > ---
> > > Changes in V4:
> > >     - Nothing changed
> > > ---
> > > Changes in V3:
> > >     - Nothing changed
> > > ---
> > > Changes in V2:
> > >     - Rename setup_trap_handler() to trap_init().
> > >     - Add Reviewed-by to the commit message.
> > > ---
> > >    xen/arch/riscv/include/asm/traps.h | 1 +
> > >    xen/arch/riscv/setup.c             | 5 +++++
> > >    xen/arch/riscv/traps.c             | 7 +++++++
> > >    3 files changed, 13 insertions(+)
> > >
> > > diff --git a/xen/arch/riscv/include/asm/traps.h
> > > b/xen/arch/riscv/include/asm/traps.h
> > > index f3fb6b25d1..f1879294ef 100644
> > > --- a/xen/arch/riscv/include/asm/traps.h
> > > +++ b/xen/arch/riscv/include/asm/traps.h
> > > @@ -7,6 +7,7 @@
> > >    
> > >    void do_trap(struct cpu_user_regs *cpu_regs);
> > >    void handle_trap(void);
> > > +void trap_init(void);
> > >    
> > >    #endif /* __ASSEMBLY__ */
> > >    
> > > diff --git a/xen/arch/riscv/setup.c b/xen/arch/riscv/setup.c
> > > index 36556eb779..b44d105b5f 100644
> > > --- a/xen/arch/riscv/setup.c
> > > +++ b/xen/arch/riscv/setup.c
> > > @@ -3,7 +3,9 @@
> > >    #include <xen/kernel.h>
> > >    
> > >    #include <asm/boot-info.h>
> > > +#include <asm/csr.h>
> > >    #include <asm/early_printk.h>
> > > +#include <asm/traps.h>
> > >    
> > >    /* Xen stack for bringing up the first CPU. */
> > >    unsigned char __initdata cpu0_boot_stack[STACK_SIZE]
> > > @@ -32,7 +34,10 @@ void __init noreturn start_xen(unsigned long
> > > bootcpu_id,
> > >    
> > >        fill_boot_info();
> > >    
> > > +    trap_init();
> > > +
> > >        early_printk("All set up\n");
> > > +
> > >        for ( ;; )
> > >            asm volatile ("wfi");
> > >    
> > > diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
> > > index 8a1529e0c5..581f34efbc 100644
> > > --- a/xen/arch/riscv/traps.c
> > > +++ b/xen/arch/riscv/traps.c
> > > @@ -13,6 +13,13 @@
> > >    #include <asm/processor.h>
> > >    #include <asm/traps.h>
> > >    
> > > +void trap_init(void)
> > > +{
> > > +    unsigned long addr = (unsigned long)&handle_trap;
> > It is not super clear to me whether this is going to store the
> > virtual
> > or physical address.
> Actually it is going to store both the virtual and physical address.
> Depending on if MMU is enabled or not.
I think some comment in the code would be really good because this is...

> > Depending on the answer, the next would be whether the value would
> > still
> > be valid after the MMU is turned on?
> It would still be valid because for addr will be generated PC-relative
> address.
... not clear to me what would guarantee that Xen is compiled with 
-noPIE. Is the cmodel?
A suggestion for the top of the function:

"Initialize the trap handling. This is called twice (before and after 
the MMU)."
And for on top of 'addr', I would add:

"When the MMU is off, this will be a physical address otherwise it would 
be a virtual address. This is guarantee because [fill the blank]".
Cheers,

--
Julien Grall