linux-kernel - [PATCH RFC v8 18/56] x86/fault: fix handle_split_page

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Date:   Mon, 20 Feb 2023 12:38:09 -0600
From:   Michael Roth <michael.roth@....com>
To:     <kvm@...r.kernel.org>
CC:     <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-crypto@...r.kernel.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
        <mingo@...hat.com>, <jroedel@...e.de>, <thomas.lendacky@....com>,
        <hpa@...or.com>, <ardb@...nel.org>, <pbonzini@...hat.com>,
        <seanjc@...gle.com>, <vkuznets@...hat.com>, <jmattson@...gle.com>,
        <luto@...nel.org>, <dave.hansen@...ux.intel.com>, <slp@...hat.com>,
        <pgonda@...gle.com>, <peterz@...radead.org>,
        <srinivas.pandruvada@...ux.intel.com>, <rientjes@...gle.com>,
        <dovmurik@...ux.ibm.com>, <tobin@....com>, <bp@...en8.de>,
        <vbabka@...e.cz>, <kirill@...temov.name>, <ak@...ux.intel.com>,
        <tony.luck@...el.com>, <marcorr@...gle.com>,
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        <alpergun@...gle.com>, <dgilbert@...hat.com>, <jarkko@...nel.org>,
        <ashish.kalra@....com>, <nikunj.dadhania@....com>,
        Hugh Dickins <hughd@...gle.com>
Subject: [PATCH RFC v8 18/56] x86/fault: fix handle_split_page_fault() to work with memfd backed pages

From: Hugh Dickins <hughd@...gle.com>

When the address is backed by a memfd, the code to split the page does
nothing more than remove the PMD from the page tables. So immediately
install a PTE to ensure that any other pages in that 2MB region are
brought back as in 4K pages.

Signed-off-by: Hugh Dickins <hughd@...gle.com>
Cc: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Ashish Kalra <ashish.kalra@....com>
Signed-off-by: Michael Roth <michael.roth@....com>
---
 mm/memory.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index e68da7e403c6..33c9020ba1f8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4999,6 +4999,11 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 static int handle_split_page_fault(struct vm_fault *vmf)
 {
 	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
+	/*
+	 * Install a PTE immediately to ensure that any other pages in
+	 * this 2MB region are brought back in as 4K pages.
+	 */
+	__pte_alloc(vmf->vma->vm_mm, vmf->pmd);
 	return 0;
 }
 
-- 
2.25.1