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Message-ID: <Zjuw2t6vL6yIcPR9@ghost>
Date: Wed, 8 May 2024 10:05:30 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Ben Dooks <ben.dooks@...ethink.co.uk>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Conor Dooley <conor.dooley@...rochip.com>,
Song Liu <song@...nel.org>, Xi Wang <xi.wang@...il.com>,
Björn Töpel <bjorn@...osinc.com>,
Clément Léger <cleger@...osinc.com>,
Jessica Clarke <jrtc27@...c27.com>,
Andy Chiu <andy.chiu@...ive.com>, linux-riscv@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/8] riscv: Add PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT
Kconfig option
On Wed, May 08, 2024 at 10:00:48AM +0100, Ben Dooks wrote:
> On 08/05/2024 02:36, Charlie Jenkins wrote:
> > The existing "RISCV_ISA_SVNAPOT" option is repurposed to be used to by
> > kernel code to determine if either
> > PLATFORM_MAY_SUPPORT_RISCV_ISA_SVNAPOT or
> > PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT has been set.
> >
> > PLATFORM_MAY_SUPPORT_RISCV_ISA_SVNAPOT will check if the hardware
> > supports Svnapot before using it, while
> > PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT will assume that the hardware
> > supports Svnapot.
> >
> > Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> > ---
> > arch/riscv/Kconfig | 19 -----------------
> > arch/riscv/Kconfig.isa | 44 ++++++++++++++++++++++++++++++++++++++++
> > arch/riscv/include/asm/pgtable.h | 3 ++-
> > 3 files changed, 46 insertions(+), 20 deletions(-)
> >
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index c2e9eded0a7d..3c1960e8cd7c 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -484,25 +484,6 @@ config RISCV_ALTERNATIVE_EARLY
> > help
> > Allows early patching of the kernel for special errata
> > -config RISCV_ISA_SVNAPOT
> > - bool "Svnapot extension support for supervisor mode NAPOT pages"
> > - depends on 64BIT && MMU
> > - depends on RISCV_ALTERNATIVE
> > - default y
> > - help
> > - Add support for the Svnapot ISA-extension in the kernel when it
> > - is detected at boot.
> > -
> > - The Svnapot extension is used to mark contiguous PTEs as a range
> > - of contiguous virtual-to-physical translations for a naturally
> > - aligned power-of-2 (NAPOT) granularity larger than the base 4KB page
> > - size. When HUGETLBFS is also selected this option unconditionally
> > - allocates some memory for each NAPOT page size supported by the kernel.
> > - When optimizing for low memory consumption and for platforms without
> > - the Svnapot extension, it may be better to say N here.
> > -
> > - If you don't know what to do here, say Y.
> > -
> > config RISCV_ISA_SVPBMT
> > bool "Svpbmt extension support for supervisor mode page-based memory types"
> > depends on 64BIT && MMU
> > diff --git a/arch/riscv/Kconfig.isa b/arch/riscv/Kconfig.isa
> > index 0663c98b5b17..37585bcd763e 100644
> > --- a/arch/riscv/Kconfig.isa
> > +++ b/arch/riscv/Kconfig.isa
> > @@ -124,3 +124,47 @@ config RISCV_ISA_V_PREEMPTIVE
> > This config allows kernel to run SIMD without explicitly disable
> > preemption. Enabling this config will result in higher memory
> > consumption due to the allocation of per-task's kernel Vector context.
> > +
> > +config RISCV_ISA_SVNAPOT
> > + bool
> > +
> > +choice
> > + prompt "Svnapot extension support for supervisor mode NAPOT pages"
> > + default PLATFORM_MAY_SUPPORT_RISCV_ISA_SVNAPOT
> > + help
> > + This selects the level of support for Svnapot in the Linux Kernel.
> > +
> > + The Svnapot extension is used to mark contiguous PTEs as a range
> > + of contiguous virtual-to-physical translations for a naturally
> > + aligned power-of-2 (NAPOT) granularity larger than the base 4KB page
> > + size. When HUGETLBFS is also selected this option unconditionally
> > + allocates some memory for each NAPOT page size supported by the kernel.
> > + When optimizing for low memory consumption and for platforms without
> > + the Svnapot extension, it may be better to prohibit Svnapot.
> > +
> > +config PROHIBIT_RISCV_ISA_SVNAPOT
> > + bool "Prohibit Svnapot extension"
> > + help
> > + Regardless of if the platform supports Svnapot, prohibit the kernel
> > + from using Svnapot.
> > +
> > +config PLATFORM_MAY_SUPPORT_RISCV_ISA_SVNAPOT
> > + bool "Allow Svnapot extension if supported"
> > + depends on 64BIT && MMU
> > + depends on RISCV_ALTERNATIVE
> > + select RISCV_ISA_SVNAPOT
> > + help
> > + Add support for the Svnapot ISA-extension in the kernel when it
> > + is detected at boot.
> > +
> > +config PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT
> > + bool "Emit Svnapot mappings when building Linux"
> > + depends on 64BIT && MMU
> > + depends on NONPORTABLE
> > + select RISCV_ISA_SVNAPOT
> > + help
> > + Compile a kernel that assumes that the platform supports Svnapot.
> > + This option produces a kernel that will not run on systems that do
> > + not support Svnapot.
> > +
> > +endchoice
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index 6afd6bb4882e..432be9691b78 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -289,7 +289,8 @@ static inline pte_t pud_pte(pud_t pud)
> > static __always_inline bool has_svnapot(void)
> > {
> > - return riscv_has_extension_likely(RISCV_ISA_EXT_SVNAPOT);
> > + return IS_ENABLED(CONFIG_PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT) ||
> > + riscv_has_extension_likely(RISCV_ISA_EXT_SVNAPOT);
>
> could you add the IS_ENABLED(*) check into riscv_has_extension_likely
> and other such functions?
I wasn't sure how to support that. An option I was debating about this
was fixing up riscv_has_extension_likely() so that it's a macro and
SVNAPOT could be expanded to both
CONFIG_PLATFORM_SUPPORTS_RISCV_ISA_SVNAPOT and RISCV_ISA_EXT_SVNAPOT.
- Charlie
>
>
> --
> Ben Dooks http://www.codethink.co.uk/
> Senior Engineer Codethink - Providing Genius
>
> https://www.codethink.co.uk/privacy.html
>
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