Messages in this thread | | | Date | Thu, 29 Jun 2023 15:47:35 -0700 (PDT) | Subject | Re: [PATCH v2 10/10] RISC-V: provide a Kconfig option to disable parsing "riscv,isa" | From | Palmer Dabbelt <> |
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On Thu, 29 Jun 2023 14:44:18 PDT (-0700), Conor Dooley wrote: > On Thu, Jun 29, 2023 at 02:16:49PM -0700, Palmer Dabbelt wrote: >> On Thu, 29 Jun 2023 13:20:55 PDT (-0700), Conor Dooley wrote: >> > On Thu, Jun 29, 2023 at 03:53:08PM +0200, Andrew Jones wrote: >> > > On Thu, Jun 29, 2023 at 12:39:51PM +0100, Conor Dooley wrote: >> > > > On Thu, Jun 29, 2023 at 11:31:33AM +0200, Andrew Jones wrote: >> > > > > On Thu, Jun 29, 2023 at 09:28:56AM +0100, Conor Dooley wrote: >> > > > > > As it says on the tin, provide a Kconfig option to disabling parsing the >> > > > > > "riscv,isa" devicetree property. Hide the option behind NONPORTABLE so >> > > > > > that only those willing to keep the pieces enable it, and make sure the >> > > > > > default kernel contains the fallback code. >> > > > > > > > > Suggested-by: Palmer Dabbelt <palmer@rivosinc.com> >> > > > > > Signed-off-by: Conor Dooley <conor.dooley@microchip.com> >> > > > > > --- >> > > > > > arch/riscv/Kconfig | 16 ++++++++++++++++ >> > > > > > arch/riscv/kernel/cpu.c | 3 +++ >> > > > > > arch/riscv/kernel/cpufeature.c | 2 +- >> > > > > > 3 files changed, 20 insertions(+), 1 deletion(-) >> > > > > > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig >> > > > > > index 1d39efe2b940..0e1909ac5947 100644 >> > > > > > --- a/arch/riscv/Kconfig >> > > > > > +++ b/arch/riscv/Kconfig >> > > > > > @@ -291,6 +291,22 @@ config NONPORTABLE >> > > > > > > > > If unsure, say N. >> > > > > > > > > +config NO_RISCV_ISA_FALLBACK >> > > > > > + bool "Permit falling back to parsing riscv,isa for extension support" >> > > > > > + depends on NONPORTABLE >> > > > > > + help >> > > > > > + Parsing the "riscv,isa" devicetree property has been deprecated and >> > > > > > + replaced by a list of explicitly defined strings. For compatibility >> > > > > > + with existing platforms, the kernel will fall back to parsing the >> > > > > > + "riscv,isa" property if the replacements are not found. >> > > > > > + >> > > > > > + Selecting Y here will result in a kernel without this fallback, and >> > > > > > + will not work on platforms where the devicetree does not contain the >> > > > > > + replacement properties of "riscv,isa-base" and >> > > > > ^ spacing issue >> > > > > Huh, weird. Given the tab followed by spaces, it must have snuck >> > > in >> > > > during reflow of the text after some rewording. >> > > > Wonder how I missed it, given that... >> >> I sometimes end up with these when reflowing in vim, the Kconfig help text >> indent confuses things (though many things confuse whatever vim reflowing >> I'm using, so I should probably find something better). > > I did it by hand, I have no excuses. > >> > > > > Should we also have a kernel command line option, 'isa_fallback', where >> > > > > without this config the command line option is not necessary to fallback, >> > > > > but, with this config, no fallback will be done unless 'isa_fallback' is >> > > > > provided? >> > > > > I don't know, maybe I have the wrong end of the stick but it >> > > feels a bit >> > > > premature for something that may never not be hidden behind NONPORTABLE? >> > > > Perhaps that could be left for a point in time where the default value >> > > > of the symbol changes, or the dependency on NONPORTABLE is removed? >> > > > >> >> I agree it might not be worth the work, but looks like that's done... > > Well, whether I did it or not doesn't mean it has to be included in the > series. The work wasn't all that much to be honest. > >> > > With the command line option, we could consider dropping NONPORTABLE (but >> > > still default off this config). What I'm thinking is that if we want to >> > > encourage the adoption of the new format, then there should be a bit of >> > > pain when it's not used, but not enough pain to risk rebellion. So, >> > > >> > > * defconfig builds will silently/painlessly fallback >> > > >> > > * builds that want to encourage adoption enable this config and will >> > > fail to boot when they don't get what they want and don't have the >> > > command line option >> > > >> > > * users still working through the growing pains can manage when >> > > the boot fails, and when it doesn't, with the command line >> > >> > So, something like the following squashed in? I inverted the config >> > option, seemed more natural that way. >> > >> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >> > index d910fba25f2c..6c0d0bc06048 100644 >> > --- a/Documentation/admin-guide/kernel-parameters.txt >> > +++ b/Documentation/admin-guide/kernel-parameters.txt >> > @@ -5437,6 +5437,13 @@ >> > [KNL] Disable ring 3 MONITOR/MWAIT feature on supported >> > CPUs. >> > + riscv_isa_fallback [RISCV] >> > + Fall back to detecting extension support using the >> > + "riscv,isa" property on devicetree systems when the >> > + replacement properties are not found, on kernels where >> > + RISCV_ISA_FALLBACK is not enabled. See the Kconfig entry >> > + for RISCV_ISA_FALLBACK. >> > + >> > ro [KNL] Mount root device read-only on boot >> > rodata= [KNL] >> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig >> > index 0370713ad965..a9a473b67182 100644 >> > --- a/arch/riscv/Kconfig >> > +++ b/arch/riscv/Kconfig >> > @@ -291,22 +291,6 @@ config NONPORTABLE >> > If unsure, say N. >> > -config NO_RISCV_ISA_FALLBACK >> > - bool "Permit falling back to parsing riscv,isa for extension support" >> > - depends on NONPORTABLE >> > - help >> > - Parsing the "riscv,isa" devicetree property has been deprecated and >> > - replaced by a list of explicitly defined strings. For compatibility >> > - with existing platforms, the kernel will fall back to parsing the >> > - "riscv,isa" property if the replacements are not found. >> > - >> > - Selecting Y here will result in a kernel without this fallback, and >> > - will not work on platforms where the devicetree does not contain the >> > - replacement properties of "riscv,isa-base" and "riscv,isa-extensions". >> > - Please see the dt-binding, located at >> > - Documentation/devicetree/bindings/riscv/extensions.yaml for details >> > - on the replacement properties. >> > - >> > choice >> > prompt "Base ISA" >> > default ARCH_RV64I >> > @@ -857,6 +841,24 @@ config XIP_PHYS_ADDR >> > be linked for and stored to. This address is dependent on your >> > own flash usage. >> > +config RISCV_ISA_FALLBACK >> > + bool "Permit falling back to parsing riscv,isa for extension support by default" >> > + default y >> >> I think the only risk here is that randconfig will result in systems that >> don't boot, but we're already stuck with no meaningful base requirements. >> Fixing that is a way bigger hurdle than this, so IMO it's fine. > > Maybe I'm way off here, but I didn't think that we had to be worried > about randconfigs not booting, as it was a testing tool?
IIRC at least some ports had randconfigs that booted, there was just some standard set of drivers always built in. We're a long way from that, though, so whatever.
>> > + help >> > + Parsing the "riscv,isa" devicetree property has been deprecated and >> > + replaced by a list of explicitly defined strings. For compatibility >> > + with existing platforms, the kernel will fall back to parsing the >> > + "riscv,isa" property if the replacements are not found. >> > + >> > + Selecting N here will result in a kernel that does not use the >> > + fallback, unless the commandline "riscv_isa_fallback" parameter is >> > + present. >> > + >> > + Please see the dt-binding, located at >> > + Documentation/devicetree/bindings/riscv/extensions.yaml for details >> > + on the replacement properties of "riscv,isa-base" and >> > + "riscv,isa-extensions". >> > + >> > endmenu # "Boot options" >> > config BUILTIN_DTB >> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h >> > index e3cda14a486b..52fa607a1691 100644 >> > --- a/arch/riscv/include/asm/hwcap.h >> > +++ b/arch/riscv/include/asm/hwcap.h >> > @@ -81,6 +81,7 @@ struct riscv_isa_ext_data { >> > extern const struct riscv_isa_ext_data riscv_isa_ext[]; >> > extern const size_t riscv_isa_ext_count; >> > +extern bool riscv_isa_fallback_cmdline; >> > >> > unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap); >> > diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c >> > index 86a1d98b8b3b..1e4cbdedc7fc 100644 >> > --- a/arch/riscv/kernel/cpu.c >> > +++ b/arch/riscv/kernel/cpu.c >> > @@ -81,7 +81,7 @@ int riscv_early_of_processor_hartid(struct device_node *node, unsigned long *har >> > return 0; >> > old_interface: >> > - if (IS_ENABLED(CONFIG_NO_RISCV_ISA_FALLBACK)) >> > + if (!IS_ENABLED(CONFIG_RISCV_ISA_FALLBACK) && !riscv_isa_fallback_cmdline) >> > return -ENODEV; >> > if (of_property_read_string(node, "riscv,isa", &isa)) { >> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c >> > index f6fb18d2af84..5d848b7c1dde 100644 >> > --- a/arch/riscv/kernel/cpufeature.c >> > +++ b/arch/riscv/kernel/cpufeature.c >> > @@ -471,6 +471,14 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap) >> > return 0; >> > } >> > +bool __initdata riscv_isa_fallback_cmdline = false; >> > +static int __init riscv_isa_fallback_setup(char *__unused) >> >> Maybe it's better to support =true and =false here? Not sure it matters, >> we're already down a rabbit hole ;) > > Dunno, not implemented a cmdline param before. Seemed "cleaner" to check > for presence, don't really care so I'll adapt to w/e. > >> > +{ >> > + riscv_isa_fallback_cmdline = true; >> > + return 1; >> > +} >> > +early_param("riscv_isa_fallback", riscv_isa_fallback_setup); >> >> IMO it's cleaner to just set the default based on the Kconfig, that way >> there's only one thing to check. We're already duplicating the "check both >> Kconfig and cmdline" logic twice, there's probably going to be others >> eventually. > > Sure. > >> > + >> > void __init riscv_fill_hwcap(void) >> > { >> > char print_str[NUM_ALPHA_EXTS + 1]; >> > @@ -490,7 +498,7 @@ void __init riscv_fill_hwcap(void) >> > } else { >> > int ret = riscv_fill_hwcap_from_ext_list(isa2hwcap); >> > - if (ret && !IS_ENABLED(CONFIG_NO_RISCV_ISA_FALLBACK)) { >> > + if (ret && (IS_ENABLED(CONFIG_RISCV_ISA_FALLBACK) || riscv_isa_fallback_cmdline)) { >> > pr_info("Falling back to deprecated \"riscv,isa\"\n"); >> > riscv_fill_hwcap_from_isa_string(isa2hwcap); >> > } >> >> I haven't read the whole patch set, but at least having a nice error for why >> probing didn't happen seems like the right way to go here. IIUC this is >> just silent when ISA string fallbacks are disabled and the new properties >> aren't there. >> > >> Sorry in advance if it's just somewhere outside the diff, though. > > It sorta is. You'll actually not even reach this code if probing fails. > Because riscv_early_of_processor_hartid(), which is called super early > on in of_parse_and_init_cpus(), checks whether there are any valid > harts (including checking for sufficient extension support to run a > kernel) we will hit a BUG() during setup_smp() & blow up really early: > > [ 0.000000] Linux version 6.4.0-rc1-00096-ge0097d2c62d5-dirty (conor@spud) (ClangBuiltLinux clang version 15.0.7 (/stuff/brsdk/llvm/clang 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a), ClangBuiltLinux LLD 15.0.7) #1 SMP PREEMPT @666 > [ 0.000000] Machine model: Microchip PolarFire-SoC Icicle Kit > [ 0.000000] SBI specification v0.3 detected > [ 0.000000] SBI implementation ID=0x1 Version=0x10000 > [ 0.000000] SBI TIME extension detected > [ 0.000000] SBI IPI extension detected > [ 0.000000] SBI RFENCE extension detected > [ 0.000000] SBI SRST extension detected > [ 0.000000] earlycon: ns16550a0 at MMIO32 0x0000000020100000 (options '115200n8') > [ 0.000000] printk: bootconsole [ns16550a0] enabled > [ 0.000000] printk: debug: skip boot console de-registration. > [ 0.000000] efi: UEFI not found. > [ 0.000000] OF: reserved mem: 0x00000000bfc00000..0x00000000bfffffff (4096 KiB) nomap non-reusable region@BFC00000 > [ 0.000000] Zone ranges: > [ 0.000000] DMA32 [mem 0x0000000080000000-0x00000000ffffffff] > [ 0.000000] Normal [mem 0x0000000100000000-0x000000107fffffff] > [ 0.000000] Movable zone start for each node > [ 0.000000] Early memory node ranges > [ 0.000000] node 0: [mem 0x0000000080000000-0x00000000bfbfffff] > [ 0.000000] node 0: [mem 0x00000000bfc00000-0x00000000bfffffff] > [ 0.000000] node 0: [mem 0x0000001040000000-0x000000107fffffff] > [ 0.000000] Initmem setup node 0 [mem 0x0000000080000000-0x000000107fffffff] > [ 0.000000] SBI HSM extension detected > [ 0.000000] CPU with hartid=0 is not available > [ 0.000000] ------------[ cut here ]------------ > [ 0.000000] kernel BUG at arch/riscv/kernel/smpboot.c:174! > [ 0.000000] Kernel BUG [#1] > [ 0.000000] Modules linked in: > [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 6.4.0-rc1-00096-ge0097d2c62d5-dirty #1 > [ 0.000000] Hardware name: Microchip PolarFire-SoC Icicle Kit (DT) > [ 0.000000] epc : of_parse_and_init_cpus+0x16c/0x16e > [ 0.000000] ra : of_parse_and_init_cpus+0x9a/0x16e > [ 0.000000] epc : ffffffff80c04e0a ra : ffffffff80c04d38 sp : ffffffff81603e20 > [ 0.000000] gp : ffffffff8182d658 tp : ffffffff81613f80 t0 : 000000000000006e > [ 0.000000] t1 : 0000000000000064 t2 : 0000000000000000 s0 : ffffffff81603e80 > [ 0.000000] s1 : 0000000000000000 a0 : 0000000000000000 a1 : 0000000000000000 > [ 0.000000] a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000 > [ 0.000000] a5 : 0000000000001fff a6 : 0000000000001fff a7 : ffffffff816148b0 > [ 0.000000] s2 : 0000000000000001 s3 : ffffffff81492a4c s4 : ffffffff81a4b090 > [ 0.000000] s5 : ffffffff81506030 s6 : 0000000000000040 s7 : 0000000000000000 > [ 0.000000] s8 : 00000000bfb6f046 s9 : 0000000000000001 s10: 0000000000000000 > [ 0.000000] s11: 00000000bf389700 t3 : 0000000000000000 t4 : 0000000000000000 > [ 0.000000] t5 : ffffffff824dd188 t6 : ffffffff824dd187 > [ 0.000000] status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003 > [ 0.000000] [<ffffffff80c04e0a>] of_parse_and_init_cpus+0x16c/0x16e > [ 0.000000] [<ffffffff80c04c96>] setup_smp+0x1e/0x26 > [ 0.000000] [<ffffffff80c03ffe>] setup_arch+0x6e/0xb2 > [ 0.000000] [<ffffffff80c00384>] start_kernel+0x72/0x400 > [ 0.000000] Code: 80e7 4a00 a603 0009 b795 1097 ffe5 80e7 92c0 9002 (9002) 715d > [ 0.000000] ---[ end trace 0000000000000000 ]--- > [ 0.000000] Kernel panic - not syncing: Fatal exception in interrupt
Thanks, I guess we can add a warning independently of these changes.
https://lore.kernel.org/r/20230629223502.1924-1-palmer@rivosinc.com/
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