Re: [PATCH v3 3/3] RISC-V: Ensure Zicbom has a valid block size

Andrew Jones
2022-11-30T11:33:31Z

On Wed, Nov 30, 2022 at 09:46:20AM +0000, Conor.Dooley@microchip.com wrote:
> On 29/11/2022 19:45, Conor Dooley wrote:
> > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> >
> > Hey Drew,
> >
> > On Tue, Nov 29, 2022 at 03:34:47PM +0100, Andrew Jones wrote:
> >> When a DT puts zicbom in the isa string, but does not provide a block
> >> size, ALT_CMO_OP() will attempt to do cache operations on address
> >> zero since the start address will be ANDed with zero. We can't simply
> >> BUG() in riscv_init_cbom_blocksize() when we fail to find a block
> >> size because the failure will happen before logging works, leaving
> >> users to scratch their heads as to why the boot hung. Instead, ensure
> >> Zicbom is disabled and output an error which will hopefully alert
> >> people that the DT needs to be fixed. While at it, add a check that
> >> the block size is a power-of-2 too.
> >>
> >> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> >> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> >
> > This seems to be failing on nommu :/ I've got host machines issues so I
> > could not reproduce it for you lcoally and paste an actual log, but if
> > you build rv64_nommu_virt_defconfig I think you should be able to
> > reproduce.
>
> The actual error is:
> riscv64-unknown-linux-gnu-ld: arch/riscv/kernel/cpufeature.o: in function `.L0 ':
> cpufeature.c:(.text.unlikely+0x8): undefined reference to `riscv_cbom_block_size'

Thanks Conor,

I'll try to get this fixed and send a v4 ASAP.

drew

>
>
> >
> > Thanks,
> > Conor.
> >
> >> Reviewed-by: Heiko Stuebner <heiko@sntech.de>
> >> ---
> >> arch/riscv/kernel/cpufeature.c | 13 +++++++++++++
> >> 1 file changed, 13 insertions(+)
> >>
> >> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> >> index 220be7222129..93e45560af30 100644
> >> --- a/arch/riscv/kernel/cpufeature.c
> >> +++ b/arch/riscv/kernel/cpufeature.c
> >> @@ -9,6 +9,7 @@
> >> #include <linux/bitmap.h>
> >> #include <linux/ctype.h>
> >> #include <linux/libfdt.h>
> >> +#include <linux/log2.h>
> >> #include <linux/module.h>
> >> #include <linux/of.h>
> >> #include <asm/alternative.h>
> >> @@ -70,6 +71,18 @@ EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
> >>
> >> static bool riscv_isa_extension_check(int id)
> >> {
> >> + switch (id) {
> >> + case RISCV_ISA_EXT_ZICBOM:
> >> + if (!riscv_cbom_block_size) {
> >> + pr_err("Zicbom detected in ISA string, but no cbom-block-size found\n");
> >> + return false;
> >> + } else if (!is_power_of_2(riscv_cbom_block_size)) {
> >> + pr_err("cbom-block-size present, but is not a power-of-2\n");
> >> + return false;
> >> + }
> >> + return true;
> >> + }
> >> +
> >> return true;
> >> }
> >>
> >> --
> >> 2.38.1
> >>
> >>
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