Re: [PATCH] MIPS: Calculate proper ebase value for 64-bit kernels

[Wu Zhangjin <wuzhangjin@gmail.com>]

On Mon, 2010-04-26 at 10:19 -0700, David Daney wrote:
> On 04/14/2010 01:03 AM, Wu Zhangjin wrote:
> > On Tue, 2010-04-13 at 18:16 +0100, Ralf Baechle wrote:
> >> On Tue, Apr 13, 2010 at 09:34:38AM +0200, Thomas Bogendoerfer wrote:
> >>
> >>> On Tue, Apr 13, 2010 at 01:03:54PM +0800, Wu Zhangjin wrote:
> >>>> This patch have broken the support to the MIPS variants whose
> >>>> cpu_has_mips_r2 is 0 for the CAC_BASE and CKSEG0 is completely different
> >>>> in these MIPSs.
> >>>
> >>> I've checked R4k and R10k manulas and the exception base is at CKSEG0, so
> >>> about CPU we are talking ? And wouldn't it make for senso to have
> >>> an extra define for the exception base then ?
> >>
> >> C0_ebase's design was a short-sigthed only considering 32-bit processors.
> >> So the exception base is in CKSEG0 on every 64-bit processor, be it R2 or
> >> older.  So yes, there is a bug as I've verified by testing but the patch
> >> is unfortunately incorrect.
> >
> > Just debugged it via PMON:
> >
> > loaded the kernel and used "g console=tty root=/dev/hda5 init=/bin/bash"
> > to start the kernel, there was a bad address exception.
> >
> > the kernel stopped at:
> >
> > Exception Cause=address error on store, SR=0x24000002, PC=0x8020526c
> > ...
> > BADVADDR=0x97ffffff80000100, ENTHI=0xfffffe000
> > ...
> > ...
> > __copy_user+0x48  ... sd  t0,0(a0)  # addr = 0x80000100 rt=0x401a8000
> >
> > Seems the a0 argument of __copy_user is _bad_.
> >
> > And tried to set a break pointer to trap_init() and per_cpu_trap_init(),
> > and then cpu_cache_init() ... r4k_cache_init() and at last found that
> > set_uncached_handler(0x100,&except_vec2_generic, 0x80);
> >
> > /*
> >   * Install uncached CPU exception handler.
> >   * This is suitable only for the cache error exception which is the only
> >   * exception handler that is being run uncached.
> >   */
> > void __cpuinit set_uncached_handler(unsigned long offset, void *addr,
> >          unsigned long size)
> > {
> > #ifdef CONFIG_32BIT
> >          unsigned long uncached_ebase = KSEG1ADDR(ebase);
> > #endif
> > #ifdef CONFIG_64BIT
> >          unsigned long uncached_ebase = TO_UNCAC(ebase);
> > #endif
> >
> >          if (!addr)
> >                  panic(panic_null_cerr);
> >
> >          memcpy((void *)(uncached_ebase + offset), addr, size);
> > }
> >
> > memcpy() called __copy_user... and the a0 is uncached_ebase + offset,
> > and uncached_ebase is defined by TO_UNCAC:
> >
> > #define TO_UNCAC(x)             (UNCAC_BASE | ((x)&  TO_PHYS_MASK))
> > #define TO_PHYS_MASK _CONST64_(0x07ffffffffffffff)
> > #define UNCAC_BASE _AC(0x9000000000000000, UL)
> >
> > If using CKSEG0 as the ebase, CKSEG0 is defined as 0xffffffff80000000,
> > then we get the address: 0x97ffffff80000100, is this address ok?
> 
> I don't think so.  We should fix TO_UNCAC() so that it works with CKSEG0 
> addresses.  It should be at physical address 0.  So 
> TO_UNCAC(0xffffffff80000000), should yield 0x9000000000000000
> 
> 
> #define TO_UNCAC(x) ({ \
> 	u64 a = (u64)(x);     \
> 	if (a & 0xffffffffc000000 == 0xffffffff80000000) \
> 		a = UNCAC_BASE | (a & 0x30000000); \
> 	else \
> 		a = UNCAC_BASE | (a & TO_PHYS_MASK) \
> 	a; \
> })

Thanks, This works with few of changes:

> diff --git a/arch/mips/include/asm/mach-generic/spaces.h b/arch/mips/include/asm/mach-generic/spaces.h
> index c9fa4b1..b49f381 100644
> --- a/arch/mips/include/asm/mach-generic/spaces.h
> +++ b/arch/mips/include/asm/mach-generic/spaces.h
> @@ -71,7 +71,14 @@
>  
>  #define TO_PHYS(x)             (             ((x) & TO_PHYS_MASK))
>  #define TO_CAC(x)              (CAC_BASE   | ((x) & TO_PHYS_MASK))
> -#define TO_UNCAC(x)            (UNCAC_BASE | ((x) & TO_PHYS_MASK))
> +#define TO_UNCAC(x)            ({ \
> +       u64 a = (u64)(x);     \
> +       if ((a & 0xffffffffc0000000UL) == 0xffffffff80000000UL) \
> +               a = UNCAC_BASE | (a & 0x30000000); \
> +       else \
> +               a = UNCAC_BASE | (a & TO_PHYS_MASK); \
> +       a; \
> +})
>  
>  #endif /* CONFIG_64BIT */

I will send it out later.

Regards,
	Wu Zhangjin

> 
> David Daney
> 
> 
> >
> > And before, we have used the CAC_BASE as the ebase, the CAC_BASE is
> > defined as following:
> >
> > #ifndef CAC_BASE
> > #ifdef CONFIG_DMA_NONCOHERENT
> > #define CAC_BASE                _AC(0x9800000000000000, UL)
> > #else
> > #define CAC_BASE                _AC(0xa800000000000000, UL)
> > #endif
> > #endif
> >
> > So, before, the uncached_base is 0x9000000000000000.
> >
> > Regards,
> > 	Wu Zhangjin
> >
> >
>