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

[Borislav Petkov]

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?

> 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.

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