RE: [PATCH v3] x86/pci-dma: add a SWIOTLB_ANY flag to lift the low mem limitation

[Miao, Jun]

>On Thu, Feb 12, 2026 at 05:37:01PM +0800, Jun Miao wrote:
>
>+ Rick.
>
>> Intel TDX guest wants to allocate a swiotlb buffer that is not
>> restricted to low memory for the trusted hypervisor scheme.  Adding a
>> new flag will be used in swiotlb_memblock_alloc() to allow allocation
>> of SWIOTLB memory beyond low memory restriction.
>>
>> Power SVM already supports this, but X86 still faces the same limitation.
>
>So?
 
Hi, Boris.
Right,  please see  8ba2ed1be90f ("swiotlb: add a SWIOTLB_ANY flag to lift the low memory restriction")

Warm regards
Jun Miao
>
>> Commit: 8ba2ed1be9 (swiotlb: add a SWIOTLB_ANY flag to lift the low
>> memory restriction)
>> Reviewed-by: Aakarsh Jain <aakarsh.jain@xxxxxxxxxxxxxxxx>
>> Tested-by: Aakarsh Jain <aakarsh.jain@xxxxxxxxxxxxxxxx>
>> Signed-off-by: Jun Miao <jun.miao@xxxxxxxxx>
>> ---
>>
>> V1 -> V2:
>> 1.Updated commit message and description.
>> 2.Add Reviewed and Tested.
>>
>> V1 Latest Feedback :
>> https://lists.openwall.net/linux-kernel/2026/02/11/483
>>
>> v2 -> v3:
>> We can alloc 4GB with the dynamic swiotlb, rather than 1GB.
>> 1G is not correct. So change the commit log.
>>
>> ---
>>  arch/x86/kernel/pci-dma.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
>> index 6267363e0189..73b9320c4a7d 100644
>> --- a/arch/x86/kernel/pci-dma.c
>> +++ b/arch/x86/kernel/pci-dma.c
>> @@ -61,7 +61,7 @@ static void __init pci_swiotlb_detect(void)
>>  	 */
>>  	if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
>>  		x86_swiotlb_enable = true;
>> -		x86_swiotlb_flags |= SWIOTLB_FORCE;
>> +		x86_swiotlb_flags |= SWIOTLB_ANY | SWIOTLB_FORCE;
>
>This is not TDX-specific but introduces a change for all encrypted guests.
>
>--
>Regards/Gruss,
>    Boris.
>
>https://people.kernel.org/tglx/notes-about-netiquette