With SEV and sometimes with SME encryption, The dma api coherent memory is typically unencrypted, meaning the linear kernel map has the encryption bit cleared. However, default page protection returned from vm_get_page_prot() has the encryption bit set. So to compute the correct page protection we need to clear the encryption bit.
Also, in order for the encryption bit setting to survive across do_mmap() and mprotect_fixup(), We need to make pgprot_modify() aware of it and not touch it. (Note that the encryption status is not logically encoded in the pfn but in the page protection even if an address line in the physical address is used). The patchset has seen some sanity testing by exporting dma_pgprot() and using it in the vmwgfx mmap handler with SEV enabled. Cc: Dave Hansen <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Christian König <[email protected]> Cc: Marek Szyprowski <[email protected]> Cc: Tom Lendacky <[email protected]>
