Re: [PATCH v1] RISC-V: take text_mutex during alternative patching

["Heiko Stübner" <heiko@sntech.de>]

Am Mittwoch, 15. Februar 2023, 15:43:10 CET schrieb Heiko Stübner:
> Hi Conor,
> 
> Am Montag, 13. Februar 2023, 23:40:38 CET schrieb Conor Dooley:
> > +CC Heiko
> > 
> > On Sun, Feb 12, 2023 at 03:08:55PM -0800, Guenter Roeck wrote:
> > > On 2/12/23 11:47, Conor Dooley wrote:
> > > > From: Conor Dooley <conor.dooley@microchip.com>
> > > > 
> > > > Guenter reported a splat during boot, that Samuel pointed out was the
> > > > lockdep assertion failing in patch_insn_write():
> > > > 
> > > > WARNING: CPU: 0 PID: 0 at arch/riscv/kernel/patch.c:63 patch_insn_write+0x222/0x2f6
> > > > epc : patch_insn_write+0x222/0x2f6
> > > >   ra : patch_insn_write+0x21e/0x2f6
> > > > epc : ffffffff800068c6 ra : ffffffff800068c2 sp : ffffffff81803df0
> > > >   gp : ffffffff81a1ab78 tp : ffffffff81814f80 t0 : ffffffffffffe000
> > > >   t1 : 0000000000000001 t2 : 4c45203a76637369 s0 : ffffffff81803e40
> > > >   s1 : 0000000000000004 a0 : 0000000000000000 a1 : ffffffffffffffff
> > > >   a2 : 0000000000000004 a3 : 0000000000000000 a4 : 0000000000000001
> > > >   a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000052464e43
> > > >   s2 : ffffffff80b4889c s3 : 000000000000082c s4 : ffffffff80b48828
> > > >   s5 : 0000000000000828 s6 : ffffffff8131a0a0 s7 : 0000000000000fff
> > > >   s8 : 0000000008000200 s9 : ffffffff8131a520 s10: 0000000000000018
> > > >   s11: 000000000000000b t3 : 0000000000000001 t4 : 000000000000000d
> > > >   t5 : ffffffffd8180000 t6 : ffffffff81803bc8
> > > > status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
> > > > [<ffffffff800068c6>] patch_insn_write+0x222/0x2f6
> > > > [<ffffffff80006a36>] patch_text_nosync+0xc/0x2a
> > > > [<ffffffff80003b86>] riscv_cpufeature_patch_func+0x52/0x98
> > > > [<ffffffff80003348>] _apply_alternatives+0x46/0x86
> > > > [<ffffffff80c02d36>] apply_boot_alternatives+0x3c/0xfa
> > > > [<ffffffff80c03ad8>] setup_arch+0x584/0x5b8
> > > > [<ffffffff80c0075a>] start_kernel+0xa2/0x8f8
> > > > 
> > > > This issue was exposed by 702e64550b12 ("riscv: fpu: switch has_fpu() to
> > > > riscv_has_extension_likely()"), as it is the patching in has_fpu() that
> > > > triggers the splats in Guenter's report.
> > > > 
> > > > Take the text_mutex before doing any code patching to satisfy lockdep.
> > > > 
> > > > Fixes: ff689fd21cb1 ("riscv: add RISC-V Svpbmt extension support")
> > > > Fixes: a35707c3d850 ("riscv: add memory-type errata for T-Head")
> > > > Fixes: 1a0e5dbd3723 ("riscv: sifive: Add SiFive alternative ports")
> > > > Reported-by: Guenter Roeck <linux@roeck-us.net>
> > > > Link: https://lore.kernel.org/all/20230212154333.GA3760469@roeck-us.net/
> > > > Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> > > 
> > > 
> > > Applying this patch together with
> > > 
> > > riscv: Fix early alternative patching
> > > riscv: Fix Zbb alternative IDs
> > > 
> > > _and_ disabling CONFIG_RISCV_ISA_ZBB fixes all problems observed with
> > > riscv64 for me. With that,
> > > 
> > > Tested-by: Guenter Roeck <linux@roeck-us.net>
> > > 
> > > Unfortunately I still see boot failures when trying to boot riscv32
> > > images, so something is still broken. I don't know yet if that is
> > > a generic problem or if it is related to a riscv patch.
> > > I am still trying to track that down ...
> > 
> > Heiko, would you be able to look at this please?
> > There's some more information in the Link: above.
> 
> just for the record, I started looking into this now.
> 
> Starting with my own code [0] on top of 6.2-rc2 I was able to verify
> - qemu-riscv32 without zbb
> - qemu-riscv32 with zbb
> - qemu-riscv64 without zbb
> - qemu-riscv64 with zbb
> to work.
> 
> So next up, I'll move over to the merged for-next branch to hopefully
> see what changed between the above and the for-next code.

So now I've also tested Palmer's for-next at
  commit ec6311919ea6 ("Merge patch series "riscv: Optimize function trace"")

again with the same variants 
- qemu-riscv32 without zbb
- qemu-riscv32 with zbb
- qemu-riscv64 without zbb
- qemu-riscv64 with zbb

And all of them booted fine into a nfs-root (debian for riscv64 and a
buildroot for riscv32).

I even forced a bug into the zbb code to make sure the patching worked
correctly (where the kernel failed as expected).

Qemu-version for me was 7.2.50 (v7.2.0-744-g5a3633929a-dirty)

I did try the one from Debian-stable (qemu-5.2) but that was too old and
didn't support Zbb yet.

One thing of note, the "active" 32bit config I had, somehow didn't produce
working images and I needed to start a new build using the rv32_defconfig.

So right now, I'm not sure what more to test though.

Heiko



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