Re: [PATCH v9 00/12] AMD broadcast TLB invalidation

[Rik van Riel]

On Thu, 2025-02-06 at 11:16 +0100, Oleksandr Natalenko wrote:
> Hello.
> 
> On čtvrtek 6. února 2025 5:43:19, středoevropský standardní čas Rik
> van Riel wrote:
> > 
> > v9:
> >  - print warning when start or end address was rounded (Peter)
> 
> OK, I've just hit one:
> 
> TLB flush not stride 200000 aligned. Start 7fffc0000000, end
> 7fffffe01000

Beautiful, the caller wants to zap 2MB pages, but
the end address is 4kB aligned.

> WARNING: CPU: 31 PID: 411 at arch/x86/mm/tlb.c:1342
> flush_tlb_mm_range+0x57b/0x600
> Modules linked in:
> CPU: 31 UID: 0 PID: 411 Comm: modprobe Not tainted 6.13.0-pf3 #1
> 1366679ca06f46d05d1e9d9c537b0c6b4c922b82
> Hardware name: ASUS System Product Name/Pro WS X570-ACE, BIOS 4902
> 08/29/2024
> RIP: 0010:flush_tlb_mm_range+0x57b/0x600
> Code: 5f e9 39 b3 3f 00 e8 24 57 f5 ff e9 e9 fc ff ff 48 8b 0c 24 4c
> 89 e2 48 c7 c7 78 59 27 b0 c6 05 3d 1a 31 02 01 e8 85 e4 01 00 <0f>
> 0b e9 35 fb ff ff fa 0f 1f 44 00 00 48 89 df e8 a0 f4 ff ff fb
> RSP: 0018:ffffc137c11e7a38 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: ffff9e6eaf1b5d80 RCX: 00000000ffffdfff
> RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
> RBP: ffff9e500244d800 R08: 00000000ffffdfff R09: ffff9e6eae1fffa8
> R10: 00000000ffffdfff R11: 0000000000000003 R12: 00007fffc0000000
> R13: 000000000000001f R14: 0000000000000015 R15: ffff9e6eaf180000
> FS:  0000000000000000(0000) GS:ffff9e6eaf180000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000000 CR3: 0000000109966000 CR4: 0000000000f50ef0
> PKRU: 55555554
> Call Trace:
>  <TASK>
>  tlb_flush_mmu+0x125/0x1a0
>  tlb_finish_mmu+0x41/0x80
>  relocate_vma_down+0x183/0x200
>  setup_arg_pages+0x201/0x390
>  load_elf_binary+0x3a7/0x17d0
>  bprm_execve+0x244/0x630
>  kernel_execve+0x180/0x1f0
>  call_usermodehelper_exec_async+0xd0/0x190
>  ret_from_fork+0x34/0x50
>  ret_from_fork_asm+0x1a/0x30
>  </TASK>
> 
> What do I do with it?

Reporting it is the right thing. Let me dig into what
setup_arg_pages and relocate_vma_down are doing to
come up with a 2MB page size area where the end is
not 2MB aligned.

Reading through the relocate_vma_down code, and the
free_pgd/p4d/pud/pmd_range code, it looks like that
code always adds PAGE_SIZE to the address being zapped,
even when zapping things at a larger granularity.

On the flip side, the code in relocate_vma_down and
free_pgd_range correctly set the TLB page size to
the 4kB PAGE_SIZE.

It looks like setting the stride_shift to something
larger is done transparently by the x86 tlb_flush()
implementation, specifically by tlb_get_unmap_shift(),
which looks at which page table level got freed to
determine what stride shift to use.

This can result in flush_tlb_mm_range being called
with a stride_shift for 2MB pages, but a range ending
on a 4kB aligned (not 2MB aligned) boundary.

Peter, how should we solve this one?

Should tlb_flush() round the start & end addresses
to match the found stride_shift?

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