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charset=koi8-r Content-Disposition: inline In-Reply-To: <20250630-x86-2level-hugetlb-v1-1-077cd53d8255@google.com> X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: F090B120009 X-Stat-Signature: 1wcgjs7dxo5yz8oai6mrr5ca4er5jzk7 X-HE-Tag: 1751315035-343153 X-HE-Meta: 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 NR03qGGx 3MssAYnU24LnFFfevj7UIVby7tl+GD4BHggP618+0h984te/MeZN1iBOTJtlAK1znWuWcGwAVrDrFeltcLZSxAGaanyFPVTWk9KUMCYLiprwYub3Wyt4vsfdDt51k78x0eGAYf3JX+ysEPgTT7tnQcG2Qs1lMfsEfci6WvmIWYeR/yMDFpyBxaJnuK206MBYdbky3nJfnp/vyWBmLbQZwbIqA9fGbcx9LzRbjCpzon+Laiw0BKD+LBid2JkxY6OZ5D4ChzF8zSwUkcC2GKc3rvRDOPygHm/XEa9cCQNeVtj635KtSOo/7mjN0meYxvfTCiGQJsKtKVdwt4qsREgkbHquV7brSCOm9vA2MNECAqOf+PzZMca3F6d07Hw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Jann, On Mon, Jun 30, 2025 at 09:07:34PM +0200, Jann Horn wrote: > Only select ARCH_WANT_HUGE_PMD_SHARE if hugetlb page table sharing is > actually possible; page table sharing requires at least three levels, > because it involves shared references to PMD tables. > > Having ARCH_WANT_HUGE_PMD_SHARE enabled on non-PAE 32-bit X86 (which > has 2-level paging) became particularly problematic after commit > 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count"), > since that changes `struct ptdesc` such that the `pt_mm` (for PGDs) and > the `pt_share_count` (for PMDs) share the same union storage - and with > 2-level paging, PMDs are PGDs. > > (For comparison, arm64 also gates ARCH_WANT_HUGE_PMD_SHARE on the > configuration of page tables such that it is never enabled with 2-level > paging.) > > Reported-by: Vitaly Chikunov > Closes: https://lore.kernel.org/r/srhpjxlqfna67blvma5frmy3aa@altlinux.org > Fixes: cfe28c5d63d8 ("x86: mm: Remove x86 version of huge_pmd_share.") > Cc: stable@vger.kernel.org > Signed-off-by: Jann Horn Tested on i586 over v6.1.142 (where the problem was surfaced). Tested-by: Vitaly Chikunov Thanks, > --- > arch/x86/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 71019b3b54ea..917f523b994b 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -147,7 +147,7 @@ config X86 > select ARCH_WANTS_DYNAMIC_TASK_STRUCT > select ARCH_WANTS_NO_INSTR > select ARCH_WANT_GENERAL_HUGETLB > - select ARCH_WANT_HUGE_PMD_SHARE > + select ARCH_WANT_HUGE_PMD_SHARE if PGTABLE_LEVELS > 2 > select ARCH_WANT_LD_ORPHAN_WARN > select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP if X86_64 > select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP if X86_64 > > --- > base-commit: d0b3b7b22dfa1f4b515fd3a295b3fd958f9e81af > change-id: 20250630-x86-2level-hugetlb-b1d8feb255ce > > -- > Jann Horn