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 44C771F5437 for ; Wed, 8 Jul 2026 11:27:29 +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=1783510050; cv=none; b=lc+Lyu8eF4lW7nT1Hfn135WCyYJBx9L1OyOGdhehHLfDUvHmXg52hqX7Mp6P88bmNxgVHjFWcKKOyDV1CHXEyoTdFV838tV1vZ4gVNXOT/0OPw5Ng2SH6oNFJ0ci1mnk69Dfj2K9P8AMe+mXuTPN5xMG/0yoY35ddJqiT9OhFd4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783510050; c=relaxed/simple; bh=vZ+R9XBVVPWOeZWKkQU4KL+E2m9NRFq5AhluHJG8hqQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=X8UjB20xpBsv1H4S+CyKbSz5uGc0J4ky8r1IIcgTOpeIJA1/7PSX8FWYoDpON9V++6aKtb9hf4q+DDHDcv85OFI6nLp5TuoZw89QeHShxc7A6Jk/9MIq4aQfIFFpJHLGEu8yXL54seVSptt8N9/aw8cVNF7okCoxlkzr9kKZibM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WeA2TjZO; 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="WeA2TjZO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3E0DF1F000E9; Wed, 8 Jul 2026 11:27:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783510049; bh=WCITo97BRAwUAgNXf7yXjLGVzL4sSosjVSJUHqOrMhw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=WeA2TjZOe252OirCjUywfqcZhOukVCQvwiAHJtWHyVmFUAAtqWOmcQZgciXa8JJrJ q/ZBtuLQ3sNNx1VLbeZPq6wV7PV5Wz2B64GalSZMQsyPA0aB5RJUGXkAnE9MIGCRPE xijPvXqEOr4SkaBWkh1OJyozMqeUZBsQyG6B7TCiAscSEvRRQECcXBqtnU4Vb6Av/n NjrqF2kLUdV94fv4YvI/U3uXlRanXVi9JbtmBQc9pB5hW+Dpf04+9UJovjOc+ThTJX v3bkXiNj6AcRzN9uWUBdNo3wdep5gkAbgNt3mn7ij0zoXWGpxR8KuwR3c9Zj2CCucG IkocKl/ql8Sgw== Message-ID: <76f24730-46de-4583-9189-ff7ba28c741d@kernel.org> Date: Wed, 8 Jul 2026 13:27:23 +0200 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: [PATCH V2] mm: Standardize printing for pgtable entries To: Ryan Roberts , Anshuman Khandual , linux-mm@kvack.org Cc: andriy.shevchenko@linux.intel.com, usama.arif@linux.dev, hughd@google.com, willy@infradead.org, Andrew Morton , linux-kernel@vger.kernel.org References: <20260708032824.969752-1-anshuman.khandual@arm.com> <25cde246-540f-4ab4-b541-0b7313c57954@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/8/26 13:22, Ryan Roberts wrote: > On 08/07/2026 04:28, Anshuman Khandual wrote: >> From: "David Hildenbrand (Arm)" >> >> Bad page map reporting currently stores page table entry values in an >> unsigned long long and prints them with fixed 64-bit-oriented format >> strings. This is inconsistent across call sites and does not work well for >> architectures where page table entry values are not naturally represented >> as 64-bit values, such as 32-bit or 128-bit entries. >> >> Introduce a common helper to convert raw page table entry values into a >> fixed-width hexadecimal string based on the actual entry size. Use it for >> bad page map reporting and for dumping the page table walk in >> __print_bad_page_map_pgtable(). >> >> Pass page table entry values to the reporting path as raw bytes together >> with their size, instead of forcing them through an unsigned long long. >> It keeps the printed output consistent and avoids truncation or misleading >> formatting for non-64-bit page table entries. >> >> Cc: Andrew Morton >> Cc: linux-mm@kvack.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: David Hildenbrand (Arm) >> Signed-off-by: Anshuman Khandual >> --- >> This patch applies on v7.2-rc2 >> >> Changes in V2: >> >> - Dropped space after ":" during print per Matthew >> - Dropped CONFIG_CPU_BIG_ENDIAN per David >> >> Changes in V1: >> >> https://lore.kernel.org/all/20260707041703.658021-1-anshuman.khandual@arm.com/ >> >> mm/memory.c | 98 ++++++++++++++++++++++++++++++++++++++++------------- >> 1 file changed, 75 insertions(+), 23 deletions(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index ff338c2abe92..a2b63af82792 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -519,9 +519,48 @@ static bool is_bad_page_map_ratelimited(void) >> return false; >> } >> >> +#define PTVAL_STR_MAX (32 + 1) /* Max 128-bit value in hex + NUL */ > > Not sure if it's worth doing something like this?: > > #define PTVAL_STR_MAX \ > (MAX(MAX(MAX(MAX(sizeof(pteval_t), sizeof(pmdval_t)), \ > sizeof(pudval_t)), \ > sizeof(p4dval_t)), \ > sizeof(pgdval_t)) + 1) > > Would probably save stack space for 32bit arches? Do we really care about that? This is about a corner cases error reporting right now. > >> + >> +static void ptval_bytes_to_hex_str(char *buf, size_t buf_size, const void *entry, size_t entry_size) >> +{ >> + if (WARN_ON_ONCE(buf_size < entry_size * 2 + 1)) { >> + snprintf(buf, buf_size, "overflow"); >> + return; >> + } >> + >> + switch (entry_size) { >> + case sizeof(u32): >> + snprintf(buf, buf_size, "%08x", *(const u32 *)entry); >> + break; >> + case sizeof(u64): >> + snprintf(buf, buf_size, "%016llx", *(const u64 *)entry); >> + break; >> +#if defined(__SIZEOF_INT128__) >> + case sizeof(u128): >> + snprintf(buf, buf_size, "%016llx%016llx", >> + (unsigned long long)(*(const u128 *)entry >> 64), >> + (unsigned long long)*(const u128 *)entry); >> + break; >> +#endif >> + default: >> + snprintf(buf, buf_size, "unsupported"); >> + break; >> + } >> +} >> + >> +#define ptval_to_str(buf, val) \ >> + do { \ >> + __auto_type __val = (val); \ >> + \ >> + ptval_bytes_to_hex_str((buf), sizeof(buf), &__val, sizeof(__val)); \ >> + } while (0) > > I think arm64 code also does pte printing, which you also need to fix up for > D128 support. Perhaps this could be moved to a header for reuse? We could do that as a second step, right? > > Also not sure if it's worth returning buf so that this pattern would be possible: > > char pmd_str[PTVAL_STR_MAX]; > pr_err("pmd=%s\n, ptval_to_str(pmd_str, pmd_val(*pmdp)); > > Although perhaps that's a bit busy and should be discouraged... Yeah, let's not do that. -- Cheers, David