From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id B4E36E55A for ; Fri, 10 Apr 2026 05:05:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775797544; cv=none; b=ZNqcC7mGil6GRrb1AcuGQ4B/BTo0/b2qCJkhXP/zMV3h+ZtMX1WIrMkPt9LLXolCL5i4KPSCYHO7R/LKOR9YPjP26ymwUynWNkcn7s9veH8iyvKtqFLbNDCzg246gEM4z2w9zajnBZpKL1HDXg9yBb+rQj1wuNNMPsjhWrIEBMM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775797544; c=relaxed/simple; bh=l0ZVxfWJ7gUGDjmiQGof6X1EzK424doNulI+ywEOOlY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=S8El6KWfkuYwfWwNAUrJy/BYhv+HKsB6j3D13LNvfkrB2N3RhINmSWvaqxCC064xly9kZ8l3wZElXMznKqUfJgCKqQIwh8YlmSTk56AJ4s8RyZZ0mSyioOlhcecghscwJa3HvJo3mH0vDDDk9uqv3gGJ6fnRw4eOqOQfYvF32KE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=r0C8PVa9; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="r0C8PVa9" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 564602008; Thu, 9 Apr 2026 22:05:36 -0700 (PDT) Received: from [10.163.181.174] (unknown [10.163.181.174]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3737E3FAF5; Thu, 9 Apr 2026 22:05:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1775797542; bh=l0ZVxfWJ7gUGDjmiQGof6X1EzK424doNulI+ywEOOlY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=r0C8PVa9cbhsNuM+1PpHIQKCsYCQoxy2vSc5vm2DvE4BqKnMfgnHzBaPqLwsqkeXN Pvu88Nyvsr+YBOTsMX/n/8n2l/4EAJOYo/gko4uK8gTzaz3ghCa7L2kqVNjZUppTRd CdWX0tZv0gDQzLDfPWwgAxs6WyGl9PvrYDCalxpA= Message-ID: Date: Fri, 10 Apr 2026 10:35:35 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC V1 07/16] arm64/mm: Convert READ_ONCE() as p4dp_get() while accessing P4D To: "David Hildenbrand (Arm)" , linux-arm-kernel@lists.infradead.org Cc: Catalin Marinas , Will Deacon , Ryan Roberts , Mark Rutland , Lorenzo Stoakes , Andrew Morton , Mike Rapoport , Linu Cherian , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com References: <20260224051153.3150613-1-anshuman.khandual@arm.com> <20260224051153.3150613-8-anshuman.khandual@arm.com> <238ab437-06b1-43ef-86bb-9341c02040b1@kernel.org> Content-Language: en-US From: Anshuman Khandual In-Reply-To: <238ab437-06b1-43ef-86bb-9341c02040b1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 08/04/26 5:47 PM, David Hildenbrand (Arm) wrote: > On 2/24/26 06:11, Anshuman Khandual wrote: >> Convert all READ_ONCE() based P4D accesses as p4dp_get() instead which will >> support both D64 and D128 translation regime going forward. >> >> Cc: Catalin Marinas >> Cc: Will Deacon >> Cc: Ryan Roberts >> Cc: Mark Rutland >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-kernel@vger.kernel.org >> Cc: kasan-dev@googlegroups.com >> Signed-off-by: Anshuman Khandual >> --- > > > [...] > >> static void __init kasan_pgd_populate(unsigned long addr, unsigned long end, >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index a80d06db4de6..16ae11b29f66 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -354,7 +354,7 @@ static int alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end, >> { >> int ret = 0; >> unsigned long next; >> - p4d_t p4d = READ_ONCE(*p4dp); >> + p4d_t p4d = p4dp_get(p4dp); >> pud_t *pudp; >> >> if (p4d_none(p4d)) { >> @@ -443,7 +443,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end, >> } >> >> do { >> - p4d_t old_p4d = READ_ONCE(*p4dp); >> + p4d_t old_p4d = p4dp_get(p4dp); >> >> next = p4d_addr_end(addr, end); >> >> @@ -453,7 +453,7 @@ static int alloc_init_p4d(pgd_t *pgdp, unsigned long addr, unsigned long end, >> goto out; >> >> BUG_ON(p4d_val(old_p4d) != 0 && >> - p4d_val(old_p4d) != READ_ONCE(p4d_val(*p4dp))); >> + p4d_val(old_p4d) != (p4d_val(p4dp_get(p4dp)))); > > Same here, while at it remove the BUG_ON. (see below) > >> >> phys += next - addr; >> } while (p4dp++, addr = next, addr != end); >> @@ -1541,7 +1541,7 @@ static void unmap_hotplug_p4d_range(pgd_t *pgdp, unsigned long addr, >> do { >> next = p4d_addr_end(addr, end); >> p4dp = p4d_offset(pgdp, addr); >> - p4d = READ_ONCE(*p4dp); >> + p4d = p4dp_get(p4dp); >> if (p4d_none(p4d)) >> continue; >> >> @@ -1703,7 +1703,7 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr, >> do { >> next = p4d_addr_end(addr, end); >> p4dp = p4d_offset(pgdp, addr); >> - p4d = READ_ONCE(*p4dp); >> + p4d = p4dp_get(p4dp); >> if (p4d_none(p4d)) >> continue; >> >> @@ -1724,7 +1724,7 @@ static void free_empty_p4d_table(pgd_t *pgdp, unsigned long addr, >> */ >> p4dp = p4d_offset(pgdp, 0UL); >> for (i = 0; i < PTRS_PER_P4D; i++) { >> - if (!p4d_none(READ_ONCE(p4dp[i]))) >> + if (!p4d_none(p4dp_get(p4dp + i))) >> return; >> } >> >> @@ -2258,4 +2258,21 @@ int pmdp_test_and_clear_young(struct vm_area_struct *vma, >> } >> #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG */ >> >> +#if CONFIG_PGTABLE_LEVELS > 3 >> +phys_addr_t pud_offset_phys(p4d_t *p4dp, unsigned long addr) >> +{ >> + p4d_t p4d = p4dp_get(p4dp); >> + >> + BUG_ON(!pgtable_l4_enabled()); > > Heh, while at it, convert that to a VM_WARN_ON_ONCE() or anything else > that is not a BUG. > > I strongly assume CONFIG_DEBUG_VM checks are sufficient. There are multiple similar BUG_ON() instances arch/arm64/include/asm/pgtable.h: BUG_ON(!pgtable_l4_enabled()); arch/arm64/include/asm/pgtable.h: BUG_ON(!pgtable_l5_enabled()); arch/arm64/mm/mmu.c: BUG_ON(pmd_val(old_pmd) != 0 && arch/arm64/mm/mmu.c: BUG_ON(pud_val(old_pud) != 0 && arch/arm64/mm/mmu.c: BUG_ON(p4d_val(old_p4d) != 0 && Shall we convert all of them as VM_WARN_ON_ONCE() in a separate patch as a pre-requisite ? > >> + >> + return p4d_page_paddr(p4d) + pud_index(addr) * sizeof(pud_t); >> +} >> + >