| Message ID | 1370646215-6543-2-git-send-email-ddaney.cavm@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Jun 07, 2013 at 04:03:05PM -0700, David Daney wrote: > Date: Fri, 7 Jun 2013 16:03:05 -0700 > From: David Daney <ddaney.cavm@gmail.com> > To: linux-mips@linux-mips.org, ralf@linux-mips.org, kvm@vger.kernel.org, > Sanjay Lal <sanjayl@kymasys.com> > Cc: linux-kernel@vger.kernel.org, David Daney <ddaney@caviumnetworks.com> > Subject: [PATCH 01/31] MIPS: Move allocate_kscratch to cpu-probe.c and make > it public. > > From: David Daney <ddaney@caviumnetworks.com> I'd just like to add a note about compatibility. Code optimized for LL/SC-less CPUs has made use of the fact that exception handlers will clobber k0/k1 to a non-zero value. On a MIPS II or better CPU a branch likely instruction could be used to atomically test k0/k1 and depending on the test, execute a store instruction like: .set noreorder beqzl $k0, ok sw $reg, offset($reg) /* if we get here, our SC emulation has failed */ ok: ... In particular Sony had elected to do this for the R5900 (after I explained the concept to somebody and told it'd be a _bad_ idea for compatibility reasons). Bad ideas are infectious so I'm sure others have used it, too. I don't think this should stop your patch nor should we unless this turns out to be an actual problem add any kludges to support such cowboy style hacks. But I wanted to mention and document the issue; maybe this should be mentioned in the log message of the next version of this patch. Acked-by: Ralf Baechle <ralf@linux-mips.org> Ralf -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Jun 14, 2013 at 01:41:18PM +0200, Ralf Baechle wrote: > Date: Fri, 14 Jun 2013 13:41:18 +0200 > From: Ralf Baechle <ralf@linux-mips.org> > To: James Hogan <james.hogan@imgtec.com> > Cc: linux-mips@linux-mips.org, kvm@vger.kernel.org, Sanjay Lal > <sanjayl@kymasys.com>, linux-kernel@vger.kernel.org, David Daney > <ddaney@caviumnetworks.com> > Subject: Re: [PATCH 01/31] MIPS: Move allocate_kscratch to cpu-probe.c and > make it public. > Content-Type: text/plain; charset=us-ascii > > On Fri, Jun 07, 2013 at 04:03:05PM -0700, David Daney wrote: > > Date: Fri, 7 Jun 2013 16:03:05 -0700 > > From: David Daney <ddaney.cavm@gmail.com> > > To: linux-mips@linux-mips.org, ralf@linux-mips.org, kvm@vger.kernel.org, > > Sanjay Lal <sanjayl@kymasys.com> > > Cc: linux-kernel@vger.kernel.org, David Daney <ddaney@caviumnetworks.com> > > Subject: [PATCH 01/31] MIPS: Move allocate_kscratch to cpu-probe.c and make > > it public. > > > > From: David Daney <ddaney@caviumnetworks.com> > > I'd just like to add a note about compatibility. Code optimized for > LL/SC-less CPUs has made use of the fact that exception handlers will > clobber k0/k1 to a non-zero value. On a MIPS II or better CPU a branch > likely instruction could be used to atomically test k0/k1 and depending > on the test, execute a store instruction like: > > .set noreorder > beqzl $k0, ok > sw $reg, offset($reg) > /* if we get here, our SC emulation has failed */ > ok: ... > > In particular Sony had elected to do this for the R5900 (after I explained > the concept to somebody and told it'd be a _bad_ idea for compatibility > reasons). Bad ideas are infectious so I'm sure others have used it, too. > > I don't think this should stop your patch nor should we unless this turns > out to be an actual problem add any kludges to support such cowboy style > hacks. But I wanted to mention and document the issue; maybe this should > be mentioned in the log message of the next version of this patch. > > Acked-by: Ralf Baechle <ralf@linux-mips.org> Bleh. I fatfingered mutt. This of course was the reply intended for "[PATCH 02/31] MIPS: Save and restore K0/K1 when CONFIG_KVM_MIPSVZ". As for 1/31: Acked-by: Ralf Baechle <ralf@linux-mips.org> Ralf -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/mips/include/asm/mipsregs.h b/arch/mips/include/asm/mipsregs.h index 87e6207..6e0da5aa 100644 --- a/arch/mips/include/asm/mipsregs.h +++ b/arch/mips/include/asm/mipsregs.h @@ -1806,6 +1806,8 @@ __BUILD_SET_C0(brcm_cmt_ctrl) __BUILD_SET_C0(brcm_config) __BUILD_SET_C0(brcm_mode) +int allocate_kscratch(void); + #endif /* !__ASSEMBLY__ */ #endif /* _ASM_MIPSREGS_H */ diff --git a/arch/mips/kernel/cpu-probe.c b/arch/mips/kernel/cpu-probe.c index c6568bf..ee1014e 100644 --- a/arch/mips/kernel/cpu-probe.c +++ b/arch/mips/kernel/cpu-probe.c @@ -1064,3 +1064,32 @@ __cpuinit void cpu_report(void) if (c->options & MIPS_CPU_FPU) printk(KERN_INFO "FPU revision is: %08x\n", c->fpu_id); } + +static DEFINE_SPINLOCK(kscratch_used_lock); + +static unsigned int kscratch_used_mask; + +int allocate_kscratch(void) +{ + int r; + unsigned int a; + + spin_lock(&kscratch_used_lock); + + a = cpu_data[0].kscratch_mask & ~kscratch_used_mask; + + r = ffs(a); + + if (r == 0) { + r = -1; + goto out; + } + + r--; /* make it zero based */ + + kscratch_used_mask |= (1 << r); +out: + spin_unlock(&kscratch_used_lock); + + return r; +} diff --git a/arch/mips/mm/tlbex.c b/arch/mips/mm/tlbex.c index ce9818e..001b87c 100644 --- a/arch/mips/mm/tlbex.c +++ b/arch/mips/mm/tlbex.c @@ -30,6 +30,7 @@ #include <linux/cache.h> #include <asm/cacheflush.h> +#include <asm/mipsregs.h> #include <asm/pgtable.h> #include <asm/war.h> #include <asm/uasm.h> @@ -307,25 +308,6 @@ static int check_for_high_segbits __cpuinitdata; static int check_for_high_segbits __cpuinitdata; -static unsigned int kscratch_used_mask __cpuinitdata; - -static int __cpuinit allocate_kscratch(void) -{ - int r; - unsigned int a = cpu_data[0].kscratch_mask & ~kscratch_used_mask; - - r = ffs(a); - - if (r == 0) - return -1; - - r--; /* make it zero based */ - - kscratch_used_mask |= (1 << r); - - return r; -} - static int scratch_reg __cpuinitdata; static int pgd_reg __cpuinitdata; enum vmalloc64_mode {not_refill, refill_scratch, refill_noscratch};