Re: [PATCH v4 6/9] mm/vmalloc: only flush the cache after the vmap succeeded

[Hao Ge <hao.ge@linux.dev>]

On 2026/11/12 08:30, Suren Baghdasaryan wrote:
> On Tue, Nov 10, 2026 at 11:25 AM Hao Ge <hao.ge@linux.dev> wrote:
>>
>> vmap_page_range() and __vmap_pages_range() call flush_cache_vmap()
> 
> New vmap_pages_range_batched() function has the same issue, so needs fixing too.

Ack. will do next version.

> 
>> before they even look at the error code. A failed mapping is never
>> used, so the flush is pointless at best.
>>
>> According to the Sashiko review it is worse than pointless on UML:
>> flush_cache_vmap() there is flush_tlb_kernel_range(), which syncs the
>> PTEs into the host OS. Flushing a half-installed mapping therefore
>> leaves host mappings behind for a range that was just freed again.
>>
>> Only flush when the mapping, and for vmap_page_range() also the KMSAN
>> metadata, is fully set up.
>>
>> Reported-by: Sashiko <sashiko-bot@kernel.org>
>> Signed-off-by: Hao Ge <hao.ge@linux.dev>
>> ---
>>  mm/vmalloc.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
>> index 0565cbfe325c..3f98056f8c7e 100644
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -369,10 +369,12 @@ int vmap_page_range(unsigned long addr, unsigned long end,
>>
>>         err = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),
>>                                  ioremap_max_page_shift);
>> -       flush_cache_vmap(addr, end);
>>         if (!err)
>>                 err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
>>                                                ioremap_max_page_shift);
>> +       if (!err)
>> +               flush_cache_vmap(addr, end);
>> +
>>         return err;
>>  }
>>
>> @@ -758,7 +760,9 @@ static int __vmap_pages_range(unsigned long addr, unsigned long end,
>>         int err;
>>
>>         err = vmap_pages_range_noflush(addr, end, prot, pages, page_shift, gfp_mask);
>> -       flush_cache_vmap(addr, end);
>> +       if (!err)
>> +               flush_cache_vmap(addr, end);
>> +
>>         return err;
>>  }
>>
>> --
>> 2.25.1
>>