Re: [PATCH v12 02/16] set_memory: add folio_{zap,restore}_direct_map helpers

From: Mike Rapoport <rppt@kernel.org>
To: Brendan Jackman <brendan.jackman@linux.dev>
Cc: "Kalyazin, Nikita" <kalyazin@amazon.co.uk>,
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Subject: Re: [PATCH v12 02/16] set_memory: add folio_{zap,restore}_direct_map helpers
Date: Fri, 3 Jul 2026 16:38:48 +0300	[thread overview]
Message-ID: <ake7aPB2O_-dAXhI@kernel.org> (raw)
In-Reply-To: <DJOUYOKL6N3R.BFIO8HEL03OA@linux.dev>

On Fri, Jul 03, 2026 at 10:19:10AM +0000, Brendan Jackman wrote:
> On Fri Apr 10, 2026 at 3:18 PM UTC, Nikita Kalyazin wrote:
> 
> My local Sashiko run pointed out that this is broken for highmem.
> 
> There's no highmem for guest_memfd but there is for secretmem.
> 
> ... but this isn't actually an issue with the patch, it's currently
> broken in Linus' master:
> 
> Su[   30.071284] ------------[ cut here ]------------
> ccessfully allocated and mapped 2097152000 bytes at 0x3a449000
> Populating memor[   30.074614] CPA: called for zero pte. vaddr = 0 cpa->vaddr = 0
> y...
> [   30.078636] WARNING: arch/x86/mm/pat/set_memory.c:1840 at __cpa_process_fault+0x34d/0x360, CPU#5: allocate_secret/570
> [   30.084789] CPU: 5 UID: 0 PID: 570 Comm: allocate_secret Not tainted 7.1.0-14063-g4edcdefd4083-dirty #10 PREEMPTLAZY
> [   30.090937] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014
> [   30.097543] EIP: __cpa_process_fault+0x34d/0x360
> [   30.100514] Code: ff ff 85 c0 0f 89 7d fe ff ff e9 3d fe ff ff 8b 03 8b 00 c7 04 24 c8 ff 64 c1 89 44 24 08 8b 45 e8 89 44 24 04 e8 53 7a 00 00 <0f> 0b c7 45 f0 f2 ff ff ff e9 fc fc ff ff 90 8d 74 26 00 55 25 00
> [   30.110829] EAX: 00000000 EBX: f64afe98 ECX: 00000000 EDX: 00000000
> [   30.114799] ESI: 00000000 EDI: f64afe98 EBP: f64afe04 ESP: f64afdcc
> [   30.118785] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 EFLAGS: 00010246
> [   30.123020] CR0: 80050033 CR2: 46c48ffc CR3: 038c8000 CR4: 00000690
> [   30.127010] Call Trace:
> [   30.129078]  __change_page_attr_set_clr+0x5e7/0x870
> [   30.132275]  ? console_unlock+0x99/0x130
> [   30.135069]  ? irq_work_queue+0x36/0x70
> [   30.137853]  ? page_address+0xd3/0xf0
> [   30.140421]  set_direct_map_invalid_noflush+0x52/0x60
> [   30.143782]  secretmem_fault+0x128/0x210
> [   30.146560]  __do_fault+0x25/0x90
> [   30.149053]  handle_mm_fault+0x6d1/0xcb0
> [   30.151759]  exc_page_fault+0x135/0x3b0
> [   30.154487]  ? doublefault_shim+0x150/0x150
> [   30.157416]  handle_exception+0x130/0x130
> [   30.160137] EIP: 0x804d29f
> [   30.162307] Code: 89 54 08 e1 89 54 08 e5 89 54 08 e9 89 54 08 ed c3 0f b6 44 24 08 89 7c 24 0c 69 c0 01 01 01 01 8b 7c 24 04 f7 c7 0f 00 00 00 <89> 44 0f fc 75 0e c1 e9 02 f3 ab 8b 44 24 04 8b 7c 24 0c c3 31 d2
> [   30.172936] EAX: 5a5a5a5a EBX: 00000000 ECX: 0c800000 EDX: 3a449000
> [   30.176927] ESI: 00000000 EDI: 3a449000 EBP: bfbbae18 ESP: bfbbadac
> [   30.180897] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00010246
> [   30.185161]  ? doublefault_shim+0x150/0x150
> [   30.187979] ---[ end trace 0000000000000000 ]---
> Bus error                  (core dumped) ./allocate_secret_i686 2000M
> 
> Fixing this directly in secretmem.c is kinda yucky but if we can just
> make folio_zap_direct_map() a NOP for highmem folios it's nice and easy
> so I propose to just fix it as a followup to this series.
> 
> Alternatively, we maybe should disable secretmem for highmem systems
> since it evidently doesn't have any users.

Yes, please :) 

-- 
Sincerely yours,
Mike.