Re: [PATCH v5 06/16] x86/tdx: Make DMA pages shared

Tom Lendacky
2021-10-20T16:33:33Z

On 10/8/21 7:37 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> Just like MKTME, TDX reassigns bits of the physical address for
> metadata. MKTME used several bits for an encryption KeyID. TDX
> uses a single bit in guests to communicate whether a physical page
> should be protected by TDX as private memory (bit set to 0) or
> unprotected and shared with the VMM (bit set to 1).
>
> __set_memory_enc_dec() is now aware about TDX and sets Shared bit
> accordingly following with relevant TDX hypercall.
>
> Also, Do TDX_ACCEPT_PAGE on every 4k page after mapping the GPA range
> when converting memory to private. Using 4k page size limit is due
> to current TDX spec restriction. Also, If the GPA (range) was
> already mapped as an active, private page, the host VMM may remove
> the private page from the TD by following the “Removing TD Private
> Pages” sequence in the Intel TDX-module specification [1] to safely
> block the mapping(s), flush the TLB and cache, and remove the
> mapping(s).
>
> BUG() if TDX_ACCEPT_PAGE fails (except "previously accepted page" case)
> , as the guest is completely hosed if it can't access memory.
>
> [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsoftware.intel.com%2Fcontent%2Fdam%2Fdevelop%2Fexternal%2Fus%2Fen%2Fdocuments%2Ftdx-module-1eas-v0.85.039.pdf&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7C0e667adf5a4042abce3908d98abd07a8%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637693367201703893%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=UGxQ9xBjWsmev7PetX%2BuS0RChkAXyaH7q6JHO9ZiUtY%3D&amp;reserved=0
>
> Tested-by: Kai Huang <kai.huang@linux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

...

> diff --git a/arch/x86/mm/mem_encrypt_common.c b/arch/x86/mm/mem_encrypt_common.c
> index f063c885b0a5..119a9056efbb 100644
> --- a/arch/x86/mm/mem_encrypt_common.c
> +++ b/arch/x86/mm/mem_encrypt_common.c
> @@ -9,9 +9,18 @@
>
> #include <asm/mem_encrypt_common.h>
> #include <linux/dma-mapping.h>
> +#include <linux/cc_platform.h>
>
> /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
> bool force_dma_unencrypted(struct device *dev)
> {
> - return amd_force_dma_unencrypted(dev);
> + if (cc_platform_has(CC_ATTR_GUEST_TDX) &&
> + cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> + return true;
> +
> + if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) ||
> + cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT))
> + return amd_force_dma_unencrypted(dev);
> +
> + return false;

Assuming the original force_dma_unencrypted() function was moved here or
cc_platform.c, then you shouldn't need any changes. Both SEV and TDX
require true be returned if CC_ATTR_GUEST_MEM_ENCRYPT returns true. And
then TDX should never return true for CC_ATTR_HOST_MEM_ENCRYPT.

> }
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 527957586f3c..6c531d5cb5fd 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -30,6 +30,7 @@
> #include <asm/proto.h>
> #include <asm/memtype.h>
> #include <asm/set_memory.h>
> +#include <asm/tdx.h>
>
> #include "../mm_internal.h"
>
> @@ -1981,8 +1982,10 @@ int set_memory_global(unsigned long addr, int numpages)
> __pgprot(_PAGE_GLOBAL), 0);
> }
>
> -static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
> +static int __set_memory_protect(unsigned long addr, int numpages, bool protect)
> {
> + pgprot_t mem_protected_bits, mem_plain_bits;
> + enum tdx_map_type map_type;
> struct cpa_data cpa;
> int ret;
>
> @@ -1997,8 +2000,25 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
> memset(&cpa, 0, sizeof(cpa));
> cpa.vaddr = &addr;
> cpa.numpages = numpages;
> - cpa.mask_set = enc ? __pgprot(_PAGE_ENC) : __pgprot(0);
> - cpa.mask_clr = enc ? __pgprot(0) : __pgprot(_PAGE_ENC);
> +
> + if (cc_platform_has(CC_ATTR_GUEST_SHARED_MAPPING_INIT)) {
> + mem_protected_bits = __pgprot(0);
> + mem_plain_bits = pgprot_cc_shared_mask();

How about having generic versions for both shared and private that return
the proper value for SEV or TDX. Then this remains looking similar to as
it does now, just replacing the __pgprot() calls with the appropriate
pgprot_cc_{shared,private}_mask().

Thanks,
Tom

> + } else {
> + mem_protected_bits = __pgprot(_PAGE_ENC);
> + mem_plain_bits = __pgprot(0);
> + }
> +
> + if (protect) {
> + cpa.mask_set = mem_protected_bits;
> + cpa.mask_clr = mem_plain_bits;
> + map_type = TDX_MAP_PRIVATE;
> + } else {
> + cpa.mask_set = mem_plain_bits;
> + cpa.mask_clr = mem_protected_bits;
> + map_type = TDX_MAP_SHARED;
> + }
> +
> cpa.pgd = init_mm.pgd;
>
> /* Must avoid aliasing mappings in the highmem code */
> @@ -2006,9 +2026,17 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
> vm_unmap_aliases();
>
> /*
> - * Before changing the encryption attribute, we need to flush caches.
> + * Before changing the encryption attribute, flush caches.
> + *
> + * For TDX, guest is responsible for flushing caches on private->shared
> + * transition. VMM is responsible for flushing on shared->private.
> */
> - cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_SME_COHERENT));
> + if (cc_platform_has(CC_ATTR_GUEST_TDX)) {
> + if (map_type == TDX_MAP_SHARED)
> + cpa_flush(&cpa, 1);
> + } else {
> + cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_SME_COHERENT));
> + }
>
> ret = __change_page_attr_set_clr(&cpa, 1);
>
> @@ -2021,18 +2049,21 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
> */
> cpa_flush(&cpa, 0);
>
> + if (!ret && cc_platform_has(CC_ATTR_GUEST_SHARED_MAPPING_INIT))
> + ret = tdx_hcall_gpa_intent(__pa(addr), numpages, map_type);
> +
> return ret;
> }
>
> int set_memory_encrypted(unsigned long addr, int numpages)
> {
> - return __set_memory_enc_dec(addr, numpages, true);
> + return __set_memory_protect(addr, numpages, true);
> }
> EXPORT_SYMBOL_GPL(set_memory_encrypted);
>
> int set_memory_decrypted(unsigned long addr, int numpages)
> {
> - return __set_memory_enc_dec(addr, numpages, false);
> + return __set_memory_protect(addr, numpages, false);
> }
> EXPORT_SYMBOL_GPL(set_memory_decrypted);
>
>