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

[Aakarsh Jain]

Hi,

Kindly requesting feedback from the x86 maintainers on this patch at 
your earliest convenience.

Thanks,
Aakarsh

On 3/18/2026 3:54 PM, Miao, Jun wrote:
> Hi Marek
> Thanks a lot for the ACK on the swiotlb.
> It is very important to confirm the functionality. I really appreciate your review @ Marek
>
> Maybe x86 maintainers would also like to hear your thoughts on this, especially since architectures like powerpc already have support for this.
> Any additional feedback or suggestions on X86 might have would be greatly appreciated.
>
> Best regards,
> Jun Miao
>
> > On 12.02.2026 10:37, Jun Miao wrote:
> > > 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.
> > > 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>
> >
> > Acked-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> >
> > > ---
> > >
> > > V1 -> V2:
> > > 1.Updated commit message and description.
> > > 2.Add Reviewed and Tested.
> > >
> > > V1 Latest Feedback :
> > > https://protect2.fireeye.com/v1/url?k=f35668f3-92dd7dc5-f357e3bc-74fe4
> > > 85cbff1-e6ff63e2f942f6a7&q=1&e=66eee4e1-a18d-47f9-ad21-
> > f3dfab1d6f09&u=
> > > https%3A%2F%2Flists.openwall.net%2Flinux-
> > kernel%2F2026%2F02%2F11%2F483
> > > 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;
> > >    	}
> > >    }
> > >    #else
> >
> > Best regards
> > --
> > Marek Szyprowski, PhD
> > Samsung R&D Institute Poland