Re: [RFC v2 28/32] x86/tdx: Make pages shared in ioremap()

[Kuppuswamy, Sathyanarayanan]

On 5/21/21 9:19 AM, Tom Lendacky wrote:
> In arch/x86/mm/mem_encrypt.c, sme_early_init() (should have renamed that
> when SEV support was added), we do:
> 	if (sev_active())
> 		swiotlb_force = SWIOTLB_FORCE;
>
> TDX should be able to do a similar thing without having to touch
> arch/x86/kernel/pci-swiotlb.c.
>
> That would remove any confusion over SME being part of a
> protected_guest_has() call.

You mean sme_active() check in arch/x86/kernel/pci-swiotlb.c is redundant?

 41 int __init pci_swiotlb_detect_4gb(void)
 42 {
 43         /* don't initialize swiotlb if iommu=off (no_iommu=1) */
 44         if (!no_iommu && max_possible_pfn > MAX_DMA32_PFN)
 45                 swiotlb = 1;
 46
 47         /*
 48          * If SME is active then swiotlb will be set to 1 so that bounce
 49          * buffers are allocated and used for devices that do not support
 50          * the addressing range required for the encryption mask.
 51          */
 52         if (sme_active() || is_tdx_guest())
 53                 swiotlb = 1;


--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer