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d="scan'208";a="107915396" Received: from unknown (HELO gm-smtp10.centrum.cz) ([46.255.225.77]) by antispam39.centrum.cz with ESMTP; 16 Apr 2025 15:53:27 +0200 Received: from arkam (ip-213-220-240-96.bb.vodafone.cz [213.220.240.96]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by gm-smtp10.centrum.cz (Postfix) with ESMTPSA id 8550480911AC; Wed, 16 Apr 2025 15:53:27 +0200 (CEST) Date: Wed, 16 Apr 2025 15:53:25 +0200 From: Petr =?utf-8?B?VmFuxJtr?= To: Matthew Wilcox Cc: Juergen Gross , linux-kernel@vger.kernel.org, Kevin Brodsky , Andrew Morton , linux-mm@kvack.org, x86@kernel.org, xen-devel@lists.xenproject.org, linux-arch@vger.kernel.org Subject: Re: Regression from a9b3c355c2e6 ("asm-generic: pgalloc: provide generic __pgd_{alloc,free}") with CONFIG_DEBUG_VM_PGFLAGS=y and Xen Message-ID: <2025416135325-Z_-2VTPsw81jMgCm-arkamar@atlas.cz> References: <202541612720-Z_-deOZTOztMXHBh-arkamar@atlas.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 42B6940014 X-Rspam-User: X-Stat-Signature: a5pkfyh36dds18dkdbiz8s9zx4s3aqjp X-HE-Tag: 1744811610-735995 X-HE-Meta: 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 vd0emBSl O5MZLsClYDFt/iuVqsNwBBsqow4v3h7QuJOSzgSVX0LZqzln7ox2T+9lMojRhCaurjj9n/vpAZfYRIkCnCD2lzpWIGbRYoF9khujMueWnA7rfKnNuzqZbSSGDFHY2842ywpQI3w/yG6aXp6EYaWKc0K9t8glvC2Y6wsyCPpw0H/SxjTQ9vWNL2uSD5F+rQEsAZt53XoBwsXfHEmpjpOSVinG9bynLeK3rlglhi6Ujm5T9EKK4xtc/Aj0ie8vnsvYL6gFFb+oGFvMQ5+DYkGVdOTQRKWu6j+bAKbJ8LFfSvzB+aBte7kPTeM9SSAQkPkW1igJMHA5M2SF0xKO+LmwI/J+vzD9XVPD3PahOcEYXzUYddfUCeik7/8+YWvVReNdK7WEdqclntI84PkVVnwzkMkmccBmDFbGPtjSQucKuxNU3xLh7LTFX/NnQDi+EYPqWjwZF X-Bogosity: Ham, tests=bogofilter, spamicity=0.000095, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 16, 2025 at 01:41:51PM +0100, Matthew Wilcox wrote: > On Wed, Apr 16, 2025 at 02:07:20PM +0200, Petr Vaněk wrote: > > I have discovered a regression introduced in commit a9b3c355c2e6 > > ("asm-generic: pgalloc: provide generic __pgd_{alloc,free}") [1,2] in > > kernel version 6.14. The problem occurs when the x86 kernel is > > configured with CONFIG_DEBUG_VM_PGFLAGS=y and is run as a PV Dom0 in Xen > > 4.19.1. During the startup, the kernel panics with the error log below. > > You also have to have CONFIG_MITIGATION_PAGE_TABLE_ISOLATION enabled > to hit this problem, otherwise we allocate an order-0 page. Indeed, the issue disappears when I disable CONFIG_MITIGATION_PAGE_TABLE_ISOLATION. > > The commit changed PGD allocation path. In the new implementation > > _pgd_alloc allocates memory with __pgd_alloc, which indirectly calls > > > > alloc_pages_noprof(gfp | __GFP_COMP, order); > > > > This is in contrast to the old behavior, where __get_free_pages was > > used, which indirectly called > > > > alloc_pages_noprof(gfp_mask & ~__GFP_HIGHMEM, order); > > > > The key difference is that the new allocator can return a compound page. > > When xen_pin_page is later called on such a page, it call > > TestSetPagePinned function, which internally uses the PF_NO_COMPOUND > > macro. This macro enforces VM_BUG_ON_PGFLAGS if PageCompound is true, > > triggering the panic when CONFIG_DEBUG_VM_PGFLAGS is enabled. > > I suspect the right thing to do here is to change the PF_NO_COMPOUND to > PF_HEAD. Probably for all of these: > > /* Xen */ > PAGEFLAG(Pinned, pinned, PF_NO_COMPOUND) > TESTSCFLAG(Pinned, pinned, PF_NO_COMPOUND) > PAGEFLAG(SavePinned, savepinned, PF_NO_COMPOUND); > PAGEFLAG(Foreign, foreign, PF_NO_COMPOUND); > PAGEFLAG(XenRemapped, xen_remapped, PF_NO_COMPOUND) > TESTCLEARFLAG(XenRemapped, xen_remapped, PF_NO_COMPOUND) > > Could you give that a try? Yes, I could. Changing PF_NO_COMPOUND to PF_HEAD in those lines resolves the issue for me. Petr