From: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
To: Huacai Chen <chenhc@lemote.com>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>,
"open list:MIPS" <linux-mips@vger.kernel.org>,
Fuxin Zhang <zhangfx@lemote.com>,
Zhangjin Wu <wuzhangjin@gmail.com>
Subject: Re: [PATCH V3 1/2] MIPS: Loongson-3: Enable COP2 usage in kernel
Date: Thu, 3 Sep 2020 10:43:31 +0200 [thread overview]
Message-ID: <20200903084331.GA7223@alpha.franken.de> (raw)
In-Reply-To: <CAAhV-H4dZMgjdHiLrebBz10J7asadErM53F+TM=fLV_66dhiLw@mail.gmail.com>
On Wed, Sep 02, 2020 at 02:54:10PM +0800, Huacai Chen wrote:
> Hi, Thomas,
>
> On Wed, Aug 26, 2020 at 8:48 PM Thomas Bogendoerfer
> <tsbogend@alpha.franken.de> wrote:
> >
> > On Fri, Aug 14, 2020 at 05:44:18PM +0800, Huacai Chen wrote:
> > > On Tue, Aug 11, 2020 at 8:08 PM Thomas Bogendoerfer
> > > <tsbogend@alpha.franken.de> wrote:
> > > > this comes with it's own memcpy/memset and stuff, I don't see a reason why
> > > > COP2 needs to be enabled there,
> > > gslq/gssq can also be generated by toolchains.
> >
> > I don't want to introduce every single CPU optimization bits into such
> > a closed first stage loader. So please use $(filter-out) in
> > arch/mips/boot/compressed/Makefile to disable creation of 16byte load/stores.
> >
> > > > which is correct for all user space process, otherwise the whole
> > > > cop2 exception thing wouldn't work. And if cop2 exception handling
> > > > has been run it's set in THREAD_STATUS.
> > > >
> > > THREAD_STATUS means thread_struct.cp0_status, which is the cp0_status
> > > when a process runs in kernel-space. KSTK_STATUS (what you have seen
> > > in copy_thread_tls() below) means cp0_status in a process's kernel
> > > stack, which saves the cp0_status when a process runs in user-space.
> > > Whether COP2 exception can work depends on that KSTK_STATUS (but not
> > > THREAD_STATUS) should not contain CU2 at the first time. So, whether
> > > or not THREAD_STATUS contains CU2, it won't break COP2 handling.
> >
> > so why don't we fix the the in-kernel cp0_status instead ?
> >
> > How about this ?
> >
> > diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> > index 90b869297893..26fb77a8d406 100644
> > --- a/arch/mips/kernel/process.c
> > +++ b/arch/mips/kernel/process.c
> > @@ -133,6 +133,7 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long usp,
> > /* Put the stack after the struct pt_regs. */
> > childksp = (unsigned long) childregs;
> > p->thread.cp0_status = read_c0_status() & ~(ST0_CU2|ST0_CU1);
> > + p->thread.cp0_status |= ST0_KERNEL_CUMASK;
> > if (unlikely(p->flags & PF_KTHREAD)) {
> > /* kernel thread */
> > unsigned long status = p->thread.cp0_status;
> I tried this way but it doesn't work, the reason is that the resume
> routine in r4k_switch.S save the current hardware status into
> THREAD_STATUS, but CU2 in hardware is cleared in its caller (i.e.,
> switch_to).
so let's fix it there:
diff --git a/arch/mips/include/asm/switch_to.h b/arch/mips/include/asm/switch_to.h
index 0b0a93bf83cd..a4374b4cb88f 100644
--- a/arch/mips/include/asm/switch_to.h
+++ b/arch/mips/include/asm/switch_to.h
@@ -117,6 +117,8 @@ do { \
__restore_dsp(next); \
} \
if (cop2_present) { \
+ u32 status = read_c0_status(); \
+ \
set_c0_status(ST0_CU2); \
if ((KSTK_STATUS(prev) & ST0_CU2)) { \
if (cop2_lazy_restore) \
@@ -127,7 +129,7 @@ do { \
!cop2_lazy_restore) { \
cop2_restore(next); \
} \
- clear_c0_status(ST0_CU2); \
+ write_c0_status(status); \
} \
__clear_r5_hw_ll_bit(); \
__clear_software_ll_bit(); \
BTW. if we come up to a final solution, this change should be a seperate
patch. And the change in process.c probably, too.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
prev parent reply other threads:[~2020-09-03 8:43 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-02 4:55 [PATCH V3 1/2] MIPS: Loongson-3: Enable COP2 usage in kernel Huacai Chen
2020-05-02 4:55 ` [PATCH V3 2/2] MIPS: Loongson-3: Calculate ra properly when unwinding the stack Huacai Chen
2020-05-06 5:29 ` [PATCH V3 1/2] MIPS: Loongson-3: Enable COP2 usage in kernel Jiaxun Yang
2020-08-01 7:59 ` Huacai Chen
2020-08-05 12:10 ` Thomas Bogendoerfer
2020-08-05 13:51 ` Jiaxun Yang
2020-08-06 1:15 ` Huacai Chen
2020-08-07 13:13 ` Thomas Bogendoerfer
2020-08-07 13:25 ` Jiaxun Yang
2020-08-07 13:36 ` Thomas Bogendoerfer
2020-08-09 14:53 ` Jiaxun Yang
2020-08-10 14:12 ` Thomas Bogendoerfer
2020-08-11 2:16 ` Jiaxun Yang
2020-08-11 6:45 ` Huacai Chen
2020-08-11 12:06 ` Thomas Bogendoerfer
2020-08-14 9:44 ` Huacai Chen
2020-08-14 13:16 ` Jiaxun Yang
2020-08-26 12:46 ` Thomas Bogendoerfer
2020-08-27 3:48 ` Huacai Chen
2020-08-28 8:42 ` Thomas Bogendoerfer
2020-08-28 9:21 ` Huacai Chen
2020-08-28 9:33 ` Thomas Bogendoerfer
2020-08-28 9:52 ` Huacai Chen
2020-08-28 11:12 ` Thomas Bogendoerfer
2020-09-02 6:54 ` Huacai Chen
2020-09-03 8:43 ` Thomas Bogendoerfer [this message]
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