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@xxxxxxx>
Signed-off-by: Jinyu Tang <tjytimi@xxxxxxx>
Signed-off-by: Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx>
---
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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