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Date: Fri, 21 Jun 2024 12:31:48 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Conor Dooley <conor.dooley@...rochip.com>,
Andrew Jones <ajones@...tanamicro.com>
Cc: Yong-Xuan Wang <yongxuan.wang@...ive.com>, linux-kernel@...r.kernel.org,
linux-riscv@...ts.infradead.org, kvm-riscv@...ts.infradead.org,
kvm@...r.kernel.org, apatel@...tanamicro.com, greentime.hu@...ive.com,
vincent.chen@...ive.com, Jinyu Tang <tjytimi@....com>,
Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
<palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
Anup Patel <anup@...infault.org>,
Mayuresh Chitale <mchitale@...tanamicro.com>,
Atish Patra <atishp@...osinc.com>, wchen <waylingii@...il.com>,
Samuel Ortiz <sameo@...osinc.com>, Clément Léger
<cleger@...osinc.com>, Evan Green <evan@...osinc.com>,
Xiao Wang <xiao.w.wang@...el.com>, Alexandre Ghiti <alexghiti@...osinc.com>,
Andrew Morton <akpm@...ux-foundation.org>,
"Mike Rapoport (IBM)" <rppt@...nel.org>,
Kemeng Shi <shikemeng@...weicloud.com>,
Samuel Holland <samuel.holland@...ive.com>,
Jisheng Zhang <jszhang@...nel.org>, Charlie Jenkins <charlie@...osinc.com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Leonardo Bras <leobras@...hat.com>
Subject: Re: [PATCH v5 1/4] RISC-V: Add Svade and Svadu Extensions Support
On 21/06/2024 12:24, Conor Dooley wrote:
> On Fri, Jun 21, 2024 at 10:43:58AM +0200, Andrew Jones wrote:
>> On Wed, Jun 05, 2024 at 08:15:07PM GMT, Yong-Xuan Wang wrote:
>>> Svade and Svadu extensions represent two schemes for managing the PTE A/D
>>> bits. When the PTE A/D bits need to be set, Svade extension intdicates
>>> that a related page fault will be raised. In contrast, the Svadu extension
>>> supports hardware updating of PTE A/D bits. Since the Svade extension is
>>> mandatory and the Svadu extension is optional in RVA23 profile, by default
>>> the M-mode firmware will enable the Svadu extension in the menvcfg CSR
>>> when only Svadu is present in DT.
>>>
>>> This patch detects Svade and Svadu extensions from DT and adds
>>> arch_has_hw_pte_young() to enable optimization in MGLRU and
>>> __wp_page_copy_user() when we have the PTE A/D bits hardware updating
>>> support.
>>>
>>> Co-developed-by: Jinyu Tang <tjytimi@....com>
>>> Signed-off-by: Jinyu Tang <tjytimi@....com>
>>> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@...ive.com>
>>> ---
>>> arch/riscv/Kconfig | 1 +
>>> arch/riscv/include/asm/csr.h | 1 +
>>> arch/riscv/include/asm/hwcap.h | 2 ++
>>> arch/riscv/include/asm/pgtable.h | 14 +++++++++++++-
>>> arch/riscv/kernel/cpufeature.c | 2 ++
>>> 5 files changed, 19 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>> index b94176e25be1..dbfe2be99bf9 100644
>>> --- a/arch/riscv/Kconfig
>>> +++ b/arch/riscv/Kconfig
>>> @@ -36,6 +36,7 @@ config RISCV
>>> select ARCH_HAS_PMEM_API
>>> select ARCH_HAS_PREPARE_SYNC_CORE_CMD
>>> select ARCH_HAS_PTE_SPECIAL
>>> + select ARCH_HAS_HW_PTE_YOUNG
>>> select ARCH_HAS_SET_DIRECT_MAP if MMU
>>> select ARCH_HAS_SET_MEMORY if MMU
>>> select ARCH_HAS_STRICT_KERNEL_RWX if MMU && !XIP_KERNEL
>>> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
>>> index 25966995da04..524cd4131c71 100644
>>> --- a/arch/riscv/include/asm/csr.h
>>> +++ b/arch/riscv/include/asm/csr.h
>>> @@ -195,6 +195,7 @@
>>> /* xENVCFG flags */
>>> #define ENVCFG_STCE (_AC(1, ULL) << 63)
>>> #define ENVCFG_PBMTE (_AC(1, ULL) << 62)
>>> +#define ENVCFG_ADUE (_AC(1, ULL) << 61)
>>> #define ENVCFG_CBZE (_AC(1, UL) << 7)
>>> #define ENVCFG_CBCFE (_AC(1, UL) << 6)
>>> #define ENVCFG_CBIE_SHIFT 4
>>> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
>>> index e17d0078a651..35d7aa49785d 100644
>>> --- a/arch/riscv/include/asm/hwcap.h
>>> +++ b/arch/riscv/include/asm/hwcap.h
>>> @@ -81,6 +81,8 @@
>>> #define RISCV_ISA_EXT_ZTSO 72
>>> #define RISCV_ISA_EXT_ZACAS 73
>>> #define RISCV_ISA_EXT_XANDESPMU 74
>>> +#define RISCV_ISA_EXT_SVADE 75
>>> +#define RISCV_ISA_EXT_SVADU 76
>>>
>>> #define RISCV_ISA_EXT_XLINUXENVCFG 127
>>>
>>> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
>>> index aad8b8ca51f1..7287ea4a6160 100644
>>> --- a/arch/riscv/include/asm/pgtable.h
>>> +++ b/arch/riscv/include/asm/pgtable.h
>>> @@ -120,6 +120,7 @@
>>> #include <asm/tlbflush.h>
>>> #include <linux/mm_types.h>
>>> #include <asm/compat.h>
>>> +#include <asm/cpufeature.h>
>>>
>>> #define __page_val_to_pfn(_val) (((_val) & _PAGE_PFN_MASK) >> _PAGE_PFN_SHIFT)
>>>
>>> @@ -288,7 +289,6 @@ static inline pte_t pud_pte(pud_t pud)
>>> }
>>>
>>> #ifdef CONFIG_RISCV_ISA_SVNAPOT
>>> -#include <asm/cpufeature.h>
>>>
>>> static __always_inline bool has_svnapot(void)
>>> {
>>> @@ -624,6 +624,18 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot)
>>> return __pgprot(prot);
>>> }
>>>
>>> +/*
>>> + * Both Svade and Svadu control the hardware behavior when the PTE A/D bits need to be set. By
>>> + * default the M-mode firmware enables the hardware updating scheme when only Svadu is present in
>>> + * DT.
>>> + */
>>> +#define arch_has_hw_pte_young arch_has_hw_pte_young
>>> +static inline bool arch_has_hw_pte_young(void)
>>> +{
>>> + return riscv_has_extension_unlikely(RISCV_ISA_EXT_SVADU) &&
>>> + !riscv_has_extension_likely(RISCV_ISA_EXT_SVADE);
>> It's hard to guess what is, or will be, more likely to be the correct
>> choice of call between the _unlikely and _likely variants. But, while we
>> assume svade is most prevalent right now, it's actually quite unlikely
>> that 'svade' will be in the DT, since DTs haven't been putting it there
>> yet. Anyway, it doesn't really matter much and maybe the _unlikely vs.
>> _likely variants are better for documenting expectations than for
>> performance.
> binding hat off, and kernel hat on, what do we actually do if there's
> neither Svadu or Svade in the firmware's description of the hardware?
> Do we just arbitrarily turn on Svade, like we already do for some
> extensions:
> /*
> * These ones were as they were part of the base ISA when the
> * port & dt-bindings were upstreamed, and so can be set
> * unconditionally where `i` is in riscv,isa on DT systems.
> */
> if (acpi_disabled) {
> set_bit(RISCV_ISA_EXT_ZICSR, isainfo->isa);
> set_bit(RISCV_ISA_EXT_ZIFENCEI, isainfo->isa);
> set_bit(RISCV_ISA_EXT_ZICNTR, isainfo->isa);
> set_bit(RISCV_ISA_EXT_ZIHPM, isainfo->isa);
> }
I'd say yes, svade just put a name on a HW mechanism that is required to
make an OS work properly (if Svadu is not present). So if a platform
only supports Svadu and it's not in the device tree, that's a bug on
their hand.
So if neither Svadu nor Svade are present in the device tree, we can
legitimately assume that Svade is enabled.
>
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> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
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