Re: [RESEND PATCH 2/2] arm64: Add encrypt/decrypt support for vmalloc regions

[Shanker Donthineni <sdonthineni@nvidia.com>]

Hi Mike

On 8/11/25 03:51, Mike Rapoport wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Sun, Aug 10, 2025 at 07:50:35PM -0500, Shanker Donthineni wrote:
>> On ARM64 systems with CCA (Confidential Compute Architecture) enabled,
>> the kernel may need to change the encryption attributes of memory
>> regions. The existing implementation of set_memory_encrypted() and
>> set_memory_decrypted() assumes that the input address is part of the
>> linear mapping region '__is_lm_address()', and fails with -EINVAL
>> otherwise.
>>
>> This breaks use cases where the memory region resides in the vmalloc
>> area, which is mapped in non-linear mapping region.
>>
>> This patch introduces a new helper, realm_set_memory(), which detects
>> whether the given address is from a non-linear mapping. If so, it uses
>> vmalloc_to_page() to resolve each page’s physical address and applies
>> attribute changes one page at a time. For the linear address regions,
>> it maintains the existing fast-path.
>>
>> This change ensures that encrypted/decrypted memory attribute updates
>> correctly for all memory regions, including those allocated via vmap(),
>> module allocations, or other vmalloc-backed paths.
>>
>> Call stack of Realm crash, QEMU hypervisor + NVME device (emulated):
>>   ...
>>   Freeing unused kernel memory: 6336K
>>   Run /sbin/init as init process
>>   Internal error: synchronous external abort: 0000000096000250 [#1]  SMP
>>   Modules linked in:
>>   CPU: 0 UID: 0 PID: 64 Comm: lsblk Not tainted 6.15.5 #2 PREEMPT(undef)
>>   Hardware name: linux,dummy-virt (DT)
>>   pstate: 43400005 (nZcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
>>   pc : __pi_memset_generic+0x16c/0x188
>>   lr : dma_alloc_from_pool+0xd0/0x1b8
>>   sp : ffff80008335b350
>>   x29: ffff80008335b350 x28: ffff800083162000 x27: ffff80008335b3c0
>>   x26: ffff80008144f000 x25: ffff8000801a27e8 x24: ffff800081e14000
>>   x23: ffffc1ffc0000000 x22: 0000000000001000 x21: ffff800081458310
>>   x20: 0000000042a40000 x19: ffff00000232fcc0 x18: 0000000000200000
>>   x17: 00000000000120c0 x16: ffff0000795520c0 x15: 0000000000000000
>>   x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
>>   x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
>>   x8 : ffff800083162000 x7 : 0000000000000000 x6 : 000000000000003f
>>   x5 : 0000000000000040 x4 : 0000000000000000 x3 : 0000000000000004
>>   x2 : 0000000000000fc0 x1 : 0000000000000000 x0 : ffff800083162000
>>   Call trace:
>>     __pi_memset_generic+0x16c/0x188 (P)
>>     dma_direct_alloc_from_pool+0xc4/0x230
>>     dma_direct_alloc+0x80/0x4a0
>>     dma_alloc_attrs+0x94/0x238
>>     dma_pool_alloc+0x128/0x258
>>     nvme_prep_rq.part.0+0x5f0/0x950
>>     nvme_queue_rq+0x78/0x1e8
>>     blk_mq_dispatch_rq_list+0x10c/0x6f0
>>     __blk_mq_sched_dispatch_requests+0x4a0/0x580
>>     blk_mq_sched_dispatch_requests+0x38/0xa0
>>     blk_mq_run_hw_queue+0x288/0x2f8
>>     blk_mq_flush_plug_list+0x134/0x630
>>     __blk_flush_plug+0x100/0x168
>>     blk_finish_plug+0x40/0x60
>>     read_pages+0x1a0/0x2b0
>>     page_cache_ra_unbounded+0x1f8/0x268
>>     force_page_cache_ra+0xa4/0xe0
>>     page_cache_sync_ra+0x48/0x268
>>     filemap_get_pages+0xf4/0x7a0
>>     filemap_read+0xf0/0x448
>>     blkdev_read_iter+0x8c/0x1a8
>>     vfs_read+0x288/0x330
>>     ksys_read+0x78/0x118
>>     __arm64_sys_read+0x24/0x40
>>     invoke_syscall+0x50/0x120
>>     el0_svc_common.constprop.0+0x48/0xf0
>>     do_el0_svc+0x24/0x38
>>     el0_svc+0x34/0xf8
>>     el0t_64_sync_handler+0x10c/0x138
>>     el0t_64_sync+0x1ac/0x1b0
>>
>> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
>> ---
>>   arch/arm64/mm/pageattr.c | 55 +++++++++++++++++++++++++++++++++++-----
>>   1 file changed, 48 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>> index 04d4a8f676db4..65c3322a86b49 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -202,21 +202,26 @@ int set_direct_map_default_noflush(struct page *page)
>>                                   PAGE_SIZE, change_page_range, &data);
>>   }
>>
>> +/*
>> + * Common function for setting memory encryption or decryption attributes.
>> + *
>> + * @addr:        Virtual start address of the memory region
>> + * @start:       Corresponding physical start address
>> + * @numpages:    Number of pages to update
>> + * @encrypt:     If true, set memory as encrypted; if false, decrypt
>> + */
>>   static int __set_memory_enc_dec(unsigned long addr,
>> +                             phys_addr_t start,
>>                                int numpages,
>>                                bool encrypt)
>>   {
>>        unsigned long set_prot = 0, clear_prot = 0;
>> -     phys_addr_t start, end;
>> +     phys_addr_t end;
>>        int ret;
>>
>>        if (!is_realm_world())
>>                return 0;
>>
>> -     if (!__is_lm_address(addr))
>> -             return -EINVAL;
>> -
>> -     start = __virt_to_phys(addr);
>>        end = start + numpages * PAGE_SIZE;
>>
>>        if (encrypt)
>> @@ -248,9 +253,45 @@ static int __set_memory_enc_dec(unsigned long addr,
>>                                      __pgprot(0));
>>   }
>>
>> +/*
>> + * Wrapper for __set_memory_enc_dec() that handles both linear-mapped
>> + * and vmalloc/module memory regions.
>> + *
>> + * If the address is in the linear map, we can directly compute the
>> + * physical address. If not (e.g. vmalloc memory), we walk each page
>> + * and call the attribute update individually.
>> + */
>> +static int realm_set_memory(unsigned long addr, int numpages, bool encrypt)
>> +{
>> +     phys_addr_t start;
>> +     struct page *page;
>> +     int ret, i;
>> +
>> +     if (__is_lm_address(addr)) {
>> +             start = __virt_to_phys(addr);
>> +             return __set_memory_enc_dec(addr, start, numpages, encrypt);
>> +     }
>> +
>> +     for (i = 0; i < numpages; i++) {
>> +             page = vmalloc_to_page((void *)addr);
>> +             if (!page)
>> +                     return -EINVAL;
> 
> It would be faster to get_vm_area(addr) and iterate over its ->pages rather
> than call vmalloc_to_page every time
> 

Thanks Mike for suggestion, I'll do it in the next patch.

>> +
>> +             start = page_to_phys(page);
>> +             ret = __set_memory_enc_dec(addr, start, 1, encrypt);
>> +             if (ret)
>> +                     return ret;
>> +
>> +             addr += PAGE_SIZE;
>> +     }
>> +
>> +     return 0;
>> +}
>> +
>>   static int realm_set_memory_encrypted(unsigned long addr, int numpages)
>>   {
>> -     int ret = __set_memory_enc_dec(addr, numpages, true);
>> +     int ret = realm_set_memory(addr, numpages, true);
>> +
>>
>>        /*
>>         * If the request to change state fails, then the only sensible cause
>> @@ -264,7 +305,7 @@ static int realm_set_memory_encrypted(unsigned long addr, int numpages)
>>
>>   static int realm_set_memory_decrypted(unsigned long addr, int numpages)
>>   {
>> -     int ret = __set_memory_enc_dec(addr, numpages, false);
>> +     int ret = realm_set_memory(addr, numpages, false);
>>
>>        WARN(ret, "Failed to decrypt memory, %d pages will be leaked",
>>             numpages);
>> --
>> 2.25.1
>>
> 
> --
> Sincerely yours,
> Mike.