Re: [PATCH v3 1/4] RISC-V: Fix compilation without RISCV_ISA_ZICBOM

[Anup Patel]

On Wed, Oct 19, 2022 at 6:01 PM Heiko Stuebner <heiko@xxxxxxxxx> wrote:
>
> Hi Anup,
>
> Am Mittwoch, 19. Oktober 2022, 14:16:19 CEST schrieb Anup Patel:
> > From: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> >
> > riscv_cbom_block_size and riscv_init_cbom_blocksize() should always
> > be available and riscv_init_cbom_blocksize() should always be
> > invoked, even when compiling without RISCV_ISA_ZICBOM enabled. This
> > is because disabling RISCV_ISA_ZICBOM means "don't use zicbom
> > instructions in the kernel" not "pretend there isn't zicbom, even
> > when there is". When zicbom is available, whether the kernel enables
> > its use with RISCV_ISA_ZICBOM or not, KVM will offer it to guests.
> > Ensure we can build KVM and that the block size is initialized even
> > when compiling without RISCV_ISA_ZICBOM.
>
> either I'm way very low on coffee or something is strange here :-) .
>
> I can fully grasp the need to init the cbom blocksize for guests, even when
> the main kernel isn't using it, but below in the patch itself it is still:

The Guest might have pass-through access to a device which is not
cache-coherent whereas Host might have all devices cache-coherent.

>
> +#ifdef CONFIG_RISCV_ISA_ZICBOM
> +void riscv_init_cbom_blocksize(void)
> +{
> [...]
>
> so the init_cbom_blocksize function is still inside a RISCV_ISA_ZICBOM
> ifdef?

Argh, I mixed changes from my previous patch and Drew's patch.

I will quickly send v4. Thanks for catching.

Regards,
Anup

>
>
> Heiko
>
>
> >
> > Fixes: 8f7e001e0325 ("RISC-V: Clean up the Zicbom block size probing")
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Signed-off-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> > ---
> >  arch/riscv/mm/cacheflush.c      | 41 +++++++++++++++++++++++++++++++++
> >  arch/riscv/mm/dma-noncoherent.c | 41 ---------------------------------
> >  2 files changed, 41 insertions(+), 41 deletions(-)
> >
> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > index 6cb7d96ad9c7..f318b2553612 100644
> > --- a/arch/riscv/mm/cacheflush.c
> > +++ b/arch/riscv/mm/cacheflush.c
> > @@ -3,6 +3,8 @@
> >   * Copyright (C) 2017 SiFive
> >   */
> >
> > +#include <linux/of.h>
> > +#include <linux/of_device.h>
> >  #include <asm/cacheflush.h>
> >
> >  #ifdef CONFIG_SMP
> > @@ -86,3 +88,42 @@ void flush_icache_pte(pte_t pte)
> >               flush_icache_all();
> >  }
> >  #endif /* CONFIG_MMU */
> > +
> > +unsigned int riscv_cbom_block_size;
> > +EXPORT_SYMBOL_GPL(riscv_cbom_block_size);
> > +
> > +#ifdef CONFIG_RISCV_ISA_ZICBOM
> > +void riscv_init_cbom_blocksize(void)
> > +{
> > +     struct device_node *node;
> > +     unsigned long cbom_hartid;
> > +     u32 val, probed_block_size;
> > +     int ret;
> > +
> > +     probed_block_size = 0;
> > +     for_each_of_cpu_node(node) {
> > +             unsigned long hartid;
> > +
> > +             ret = riscv_of_processor_hartid(node, &hartid);
> > +             if (ret)
> > +                     continue;
> > +
> > +             /* set block-size for cbom extension if available */
> > +             ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
> > +             if (ret)
> > +                     continue;
> > +
> > +             if (!probed_block_size) {
> > +                     probed_block_size = val;
> > +                     cbom_hartid = hartid;
> > +             } else {
> > +                     if (probed_block_size != val)
> > +                             pr_warn("cbom-block-size mismatched between harts %lu and %lu\n",
> > +                                     cbom_hartid, hartid);
> > +             }
> > +     }
> > +
> > +     if (probed_block_size)
> > +             riscv_cbom_block_size = probed_block_size;
> > +}
> > +#endif
> > diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
> > index b0add983530a..d919efab6eba 100644
> > --- a/arch/riscv/mm/dma-noncoherent.c
> > +++ b/arch/riscv/mm/dma-noncoherent.c
> > @@ -8,13 +8,8 @@
> >  #include <linux/dma-direct.h>
> >  #include <linux/dma-map-ops.h>
> >  #include <linux/mm.h>
> > -#include <linux/of.h>
> > -#include <linux/of_device.h>
> >  #include <asm/cacheflush.h>
> >
> > -unsigned int riscv_cbom_block_size;
> > -EXPORT_SYMBOL_GPL(riscv_cbom_block_size);
> > -
> >  static bool noncoherent_supported;
> >
> >  void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
> > @@ -77,42 +72,6 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> >       dev->dma_coherent = coherent;
> >  }
> >
> > -#ifdef CONFIG_RISCV_ISA_ZICBOM
> > -void riscv_init_cbom_blocksize(void)
> > -{
> > -     struct device_node *node;
> > -     unsigned long cbom_hartid;
> > -     u32 val, probed_block_size;
> > -     int ret;
> > -
> > -     probed_block_size = 0;
> > -     for_each_of_cpu_node(node) {
> > -             unsigned long hartid;
> > -
> > -             ret = riscv_of_processor_hartid(node, &hartid);
> > -             if (ret)
> > -                     continue;
> > -
> > -             /* set block-size for cbom extension if available */
> > -             ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
> > -             if (ret)
> > -                     continue;
> > -
> > -             if (!probed_block_size) {
> > -                     probed_block_size = val;
> > -                     cbom_hartid = hartid;
> > -             } else {
> > -                     if (probed_block_size != val)
> > -                             pr_warn("cbom-block-size mismatched between harts %lu and %lu\n",
> > -                                     cbom_hartid, hartid);
> > -             }
> > -     }
> > -
> > -     if (probed_block_size)
> > -             riscv_cbom_block_size = probed_block_size;
> > -}
> > -#endif
> > -
> >  void riscv_noncoherent_supported(void)
> >  {
> >       WARN(!riscv_cbom_block_size,
> >
>
>
>
>