Messages in this thread |  | | Subject | Re: [RFC v2 28/32] x86/tdx: Make pages shared in ioremap() | | From | Tom Lendacky <> | | Date | Wed, 26 May 2021 17:14:05 -0500 |
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On 5/26/21 5:02 PM, Tom Lendacky wrote: > On 5/26/21 4:37 PM, Kuppuswamy, Sathyanarayanan wrote: >> >> >> 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? > > No, the sme_active() check is required to make sure that SWIOTLB is > available under SME. Encrypted DMA is supported under SME if the device > supports 64-bit DMA. But if the device doesn't support 64-bit DMA and the > IOMMU is not active, then DMA will be bounced through SWIOTLB. > > As compared to SEV, where all DMA has to be bounced through SWIOTLB or > unencrypted memory. For that, swiotlb_force is used.
I should probably add that SME is memory encryption support for host/hypervisor/bare-metal, while SEV is memory encryption support for virtualization.
Thanks, Tom
> > Thanks, > Tom > >> >> 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; >> >>
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