From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 544E32F5A36 for ; Tue, 8 Sep 2026 04:09:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788840541; cv=none; b=nlfICLk8UKQVjuVhEMb8Zyj4lhjYWn81/5Ie54Csujb0SgvvDp+XuXKP6AzUJ3GLjdBKnJTPnmrZDt1o+xGzBMvYccGGKb6sRiDWP7JrF/ar8tqUK7s04ScwnZiOJWCfE3FtjGO5k4bKxIsmHNTPloYWtW1QZgfn0yQ4ftkfCiA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788840541; c=relaxed/simple; bh=LgzuqXsiLqBrdZtyeXUWFV/L3O7GIAF6Te0OjwEMB0g=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nDDPWUbJ/3nQHjLZkaB49XmoInFIbGRKAy39BEbolech6WI+ZmhGvWVPUO4Lh3x5hw+3nkaFS68cW1GnYEjt/sJkiwTMab+QSMD44USqmD4Odx47j/jzI4GaQCME2vCuV389nvivA1pIFwHhOc9kDMxHzW9hJHDCCoOtYRBmV8w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ag5CVwaZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ag5CVwaZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2C981F00A3A; Tue, 8 Sep 2026 04:08:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788840539; bh=ehoCTMx0coj/KJ47b9XcGVJUZU+ZQz9X4iinIICsjVQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=ag5CVwaZAQZNPeajC7pqJrW85pxzfgItMgDVZ1etA4SCzqeijDvQZyE0kpC3yK6TF Kuc+cXadqnt2UTUgZi5/Mwa9JuWe2qNPKLJ3NiA4TdPpl3bfHdpcucFD752xYOb75b mZEySrspBLVmu8NwVPTWzOtefb0H2IV++NdZ8OyN3XGYTddP2Z2ddLR0/RM6gPL0Bx 5Hg7H/eT154Ue0vKTEO9//UifTXcGJ2WtoZs5XlUTit9KAPuS43sUUgc5fx1E8c/oq BKJsz3/4w7Tl8StirlH3w0ZBqZwn1DFHSyRXiOWPbnDrLiKQ0p5XHHhi6jfAGgCvHl d0zeVd+L/Owkg== Date: Tue, 8 Sep 2026 11:49:10 +0800 From: Jisheng Zhang To: Conor Dooley Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Andrey Ryabinin , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com Subject: Re: [PATCH v2 4/5] riscv: RISCV_ISA_SV48 and RISCV_ISA_SV57 under NONPORTABLE Message-ID: References: <20260907151437.7603-1-jszhang@kernel.org> <20260907151437.7603-5-jszhang@kernel.org> <20260907-backless-theatrics-f19e489bc63f@spud> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260907-backless-theatrics-f19e489bc63f@spud> On Mon, Sep 07, 2026 at 05:21:11PM +0100, Conor Dooley wrote: > On Mon, Sep 07, 2026 at 11:14:36PM +0800, Jisheng Zhang wrote: > > In last commit, we have optimized the pgtable_l4|l5_enabled with isa > > extension alternative mechanism, thus a typical access_ok(addr, 1); > > is compiled as: > > > > ffffffff8001dd30: 1141 addi sp,sp,-16 > > ffffffff8001dd32: e022 sd s0,0(sp) > > ffffffff8001dd34: e406 sd ra,8(sp) > > ffffffff8001dd36: 0800 addi s0,sp,16 > > ffffffff8001dd38: 00000013 nop > > ffffffff8001dd3c: 02a0006f j ffffffff8001dd66 > > ffffffff8001dd40: 60a2 ld ra,8(sp) > > ffffffff8001dd42: 6402 ld s0,0(sp) > > ffffffff8001dd44: 57fd li a5,-1 > > ffffffff8001dd46: 83a1 srli a5,a5,0x8 > > ffffffff8001dd48: 00a7b533 sltu a0,a5,a0 > > ffffffff8001dd4c: 00154513 xori a0,a0,1 > > ffffffff8001dd50: 0141 addi sp,sp,16 > > ffffffff8001dd52: 8082 ret > > ... > > ffffffff8001dd64: bfe1 j ffffffff8001dd3c > > ffffffff8001dd66: 0180006f j ffffffff8001dd7e > > ffffffff8001dd6a: 60a2 ld ra,8(sp) > > ffffffff8001dd6c: 6402 ld s0,0(sp) > > ffffffff8001dd6e: 57fd li a5,-1 > > ffffffff8001dd70: 83c5 srli a5,a5,0x11 > > ffffffff8001dd72: 00a7b533 sltu a0,a5,a0 > > ffffffff8001dd76: 00154513 xori a0,a0,1 > > ffffffff8001dd7a: 0141 addi sp,sp,16 > > ffffffff8001dd7c: 8082 ret > > ffffffff8001dd7e: 60a2 ld ra,8(sp) > > ffffffff8001dd80: 6402 ld s0,0(sp) > > ffffffff8001dd82: 57fd li a5,-1 > > ffffffff8001dd84: 83e9 srli a5,a5,0x1a > > ffffffff8001dd86: 00a7b533 sltu a0,a5,a0 > > ffffffff8001dd8a: 00154513 xori a0,a0,1 > > ffffffff8001dd8e: 0141 addi sp,sp,16 > > ffffffff8001dd90: 8082 ret > > > > As can be seen, different branches for SV39/SV48/SV57 are still there, > > since access_ok() sits at hot code path, why not reduce the code size > > to optimize to make the instruction cache happy? > > > > Introduce RISCV_ISA_SV48 and RISCV_ISA_SV57 under NONPORTABLE, so that > > the embedded platforms can choose the best option themselves, while > > still keep the feature of unified one kernel Image for all SV39, SV48 > > and SV57. > > > > Before the patch, vmlinux built with pure RISCV64 defconfig > > text data bss dec hex filename > > 13439437 6790446 483221 20713104 13c0e90 /tmp/old/vmlinux > > > > After the patch, vmlinux built with pure RISCV64 defconfig: > > text data bss dec hex filename > > 13314445 6787934 466837 20569216 139dc80 /tmp/new/vmlinux > > > > .text section is reduced by 122KB! > > > > And after the patch, typical access_ok(addr, 1) is compiled as: > > ffffffff8001809a: 1141 addi sp,sp,-16 > > ffffffff8001809c: e022 sd s0,0(sp) > > ffffffff8001809e: e406 sd ra,8(sp) > > ffffffff800180a0: 0800 addi s0,sp,16 > > ffffffff800180a2: 00000013 nop > > ffffffff800180a6: 60a2 ld ra,8(sp) > > ffffffff800180a8: 6402 ld s0,0(sp) > > ffffffff800180aa: 4785 li a5,1 > > ffffffff800180ac: 179a slli a5,a5,0x26 > > ffffffff800180ae: 00f53533 sltu a0,a0,a5 > > ffffffff800180b2: 0141 addi sp,sp,16 > > ffffffff800180b4: 8082 ret > > > > only 12 instruction!! For refernece, before the patch, the access(addr, > > 1) needs 32 instructions. > > > > Signed-off-by: Jisheng Zhang > > --- > > arch/riscv/Kconfig | 24 ++++++++++++++++++++++++ > > arch/riscv/include/asm/pgtable-64.h | 12 ++++++++++++ > > arch/riscv/mm/init.c | 10 ++++++++++ > > 3 files changed, 46 insertions(+) > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > index e9476b8cbeb0..4cdb1e3f34be 100644 > > --- a/arch/riscv/Kconfig > > +++ b/arch/riscv/Kconfig > > @@ -602,6 +602,30 @@ config RISCV_ISA_SSQOSID > > cache partitioning scheme and use the MCID to track how much > > cache a process, or a group of processes, is using. > > > > +config RISCV_ISA_SV48 > > + bool "Page-Based 48-bit Virtual-Memory System" > > + depends on 64BIT && NONPORTABLE > > + default y > > I don't understand how you've got this set up here. > If this is genuinely non-portable, then you should not set the default to > enabled. However, I'm not really sure that this is actually non-portable > at all.... > > > + help > > + Add support for the Page-Based 48-bit Virtual-Memory System. > > + > > + Enable this option for systems for which a 39-bit virtual address > > + space is insufficient. But if 39-bit is enough, disabling this > > + option will result in smaller kernel size and slighly better > > + performance. > > + > > +config RISCV_ISA_SV57 > > + bool "Page-Based 57-bit Virtual-Memory System" > > + depends on 64BIT && NONPORTABLE > > + default y > > + help > > + Add support for the Page-Based 57-bit Virtual-Memory System. > > + > > + Enable this option for systems for which a 48-bit virtual address > > + space is insufficient. But if 48-bit is enough, disabling this > > + option will result in smaller kernel size and slighly better > > + performance. > > + > > config RISCV_ISA_SVPBMT > > bool "Svpbmt extension support for supervisor mode page-based memory types" > > depends on 64BIT && MMU > > diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h > > index 7e30ec0e9f6c..f2d29da93eea 100644 > > --- a/arch/riscv/include/asm/pgtable-64.h > > +++ b/arch/riscv/include/asm/pgtable-64.h > > @@ -16,21 +16,33 @@ extern bool _pgtable_l5_enabled; > > #ifdef USE_EARLY_PGTABLE_LEVELS > > static __always_inline bool pgtable_l5_enabled(void) > > { > > + if (IS_ENABLED(CONFIG_NONPORTABLE) && !IS_ENABLED(CONFIG_RISCV_ISA_SV57)) > > + return false; > > + > > return _pgtable_l5_enabled; > > } > > > > static __always_inline bool pgtable_l4_enabled(void) > > { > > + if (IS_ENABLED(CONFIG_NONPORTABLE) && !IS_ENABLED(CONFIG_RISCV_ISA_SV48)) > > + return false; > > + > > return _pgtable_l4_enabled; > > } > > #else > > static __always_inline bool pgtable_l4_enabled(void) > > { > > + if (IS_ENABLED(CONFIG_NONPORTABLE) && !IS_ENABLED(CONFIG_RISCV_ISA_SV48)) > > + return false; > > + > > return riscv_has_extension_likely(RISCV_ISA_EXT_SV48); > > } > > > > static __always_inline bool pgtable_l5_enabled(void) > > { > > + if (IS_ENABLED(CONFIG_NONPORTABLE) && !IS_ENABLED(CONFIG_RISCV_ISA_SV57)) > > + return false; > > + > > return riscv_has_extension_likely(RISCV_ISA_EXT_SV57); > > } > > #endif > > ...because the code here won't enable sv57 etc if not supported... > > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > > index 2a2402d79bc4..90bb85c5f167 100644 > > --- a/arch/riscv/mm/init.c > > +++ b/arch/riscv/mm/init.c > > @@ -844,6 +844,16 @@ static __init void set_satp_mode(uintptr_t dtb_pa) > > > > kernel_map.page_offset = PAGE_OFFSET_L5; > > > > + /* Fall back to Sv48 if Sv57 is unsupported on non-portable systems */ > > + if (IS_ENABLED(CONFIG_NONPORTABLE) && !IS_ENABLED(CONFIG_RISCV_ISA_SV57) && > > + satp_mode_limit == 0) > > + satp_mode_limit = SATP_MODE_48; > > ...and neither does the code here. > > > Introduce RISCV_ISA_SV48 and RISCV_ISA_SV57 under NONPORTABLE, so that > > the embedded platforms can choose the best option themselves, while > > still keep the feature of unified one kernel Image for all SV39, SV48 > > and SV57. > > NONPORTABLE is what you're meant to depend on when the kernel that gets > built cannot run on platforms without the feature. The reason I put these two Kconfig options under NONPORTABLE is: all distributions won't enable NONPORTABLE for their defconfig, and I guess the distributions want to kept unified one kernel Image for all SV39, SV48 and SV57. I have no preference whether move them out of NONPORTABLE or not. > > > + > > + /* Fall back to Sv39 if Sv48 is unsupported on non-portable systems */ > > + if (IS_ENABLED(CONFIG_NONPORTABLE) && !IS_ENABLED(CONFIG_RISCV_ISA_SV48) && > > + satp_mode_limit == SATP_MODE_48) > > + satp_mode_limit = SATP_MODE_39; > > + > > if (satp_mode_limit == SATP_MODE_48) { > > disable_pgtable_l5(); > > } else if (satp_mode_limit == SATP_MODE_39) { > > -- > > 2.53.0 > >