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b=G9DmyQJlYXMGxO+kJ58x5iAqxVtHA1mCBKq7KNZdvUlWR9XJ5HaEtnQyLfTa7O6wd LzYopOaIa5luNcZ6t0F2z5rKjyAzIj30XndYk7TjG3ZCXcUij+GYhlWIuSn9rptISU mftiKy/GY8GKpiUP6hHnEm6bkVa5iNFUZhZNeHVPKD8ewpOTuA039+1E+VTUK43Y5h vELvAES6yBe85FPFcqP70xoeis8ECjERLaHMkidindQ1MZROLNj2Mj/gI8Ylq2u+cS W1shudVIGjfNLLrOAywROLUzVmX2SL8VkMTXLT9B1eLeDArlK6NoF00A4zg5hW7yFv JOw4DrvLpLjXw== Date: Tue, 18 Aug 2026 00:30:15 +0000 From: Yosry Ahmed To: Brendan Jackman Cc: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Vlastimil Babka , Mike Rapoport , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, Sumit Garg , Will Deacon , rientjes@google.com, "Kalyazin, Nikita" , patrick.roy@linux.dev, "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Sean Christopherson Subject: Re: [PATCH v3 04/26] x86/mm: split out preallocate_sub_pgd() Message-ID: References: <20260726-page_alloc-unmapped-v3-0-6f5729aa9832@google.com> <20260726-page_alloc-unmapped-v3-4-6f5729aa9832@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: pbmg839mmg697hn1rjgquznrfhofdaao X-Rspamd-Queue-Id: CEECE40009 X-Rspamd-Server: rspam03 X-Rspam-User: X-HE-Tag: 1787013018-477468 X-HE-Meta: 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 qRMrb11h olvT/H2TbNuQWpqX80nD+8xOEuZiriLComfDuYpLPtX9sUhQQacergxncaFHsFBko3caWc6IYXXOhxMaswORJxbJVJ1rF+7cW2aT/krae+7BLTCpWdCxxVmFcgcwpobd+p0xww6BgQTNXASlNt6cU9jftyC8AoHnkPPHYVaoD0PLjH8YlWIXguAI2K2upTOyyL040H9rM8RtAI6b4jjGmlW66XbdFqt+zFFvuTfVKecAG7vWGGnzchotEQTUOV3mMh1oIkkZmBIgVwXXEkBA4dz1fIfn0Kx2W0HYBvKx+77/wsT7XKjCH2cGH4ySB03oX/Dzs08nq0fz5jPc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > >> + > >> + /* > >> + * On 4-level systems, the P4D layer is folded away and > >> + * the above code does no preallocation. Below, go down > >> + * to the pud _software_ level to ensure the second > >> + * hardware level is allocated on 4-level systems too. > >> + */ > >> + lvl = "pud"; > >> + pud = pud_alloc(mm, p4d, addr); > >> + if (!pud) > >> + goto failed; > >> + return 0; > >> + > >> +failed: > >> + pr_warn_ratelimited("Failed to preallocate %s\n", lvl); > > > > Can this possibly fire more than once? IIUC we will panic right after > > returning. > > In the immediate usecase no, but once it's used for > mm_local_map_to_user() we do actually handle failure. Oh yeah I missed this, thanks.