Re: [PATCH v5 04/16] x86/tdx: Make pages shared in ioremap()

[Tom Lendacky <thomas.lendacky@amd.com>]

On 10/8/21 7:36 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> 
> All ioremap()ed pages that are not backed by normal memory (NONE or
> RESERVED) have to be mapped as shared.
> 
> Reuse the infrastructure from AMD SEV code.
> 
> Note that DMA code doesn't use ioremap() to convert memory to shared as
> DMA buffers backed by normal memory. DMA code make buffer shared with
> set_memory_decrypted().
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.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>
> ---
> 
> Changes since v4:
>   * Renamed "protected_guest" to "cc_guest".
>   * Replaced use of prot_guest_has() with cc_guest_has()
>   * Modified the patch to adapt to latest version cc_guest_has()
>     changes.
> 
> Changes since v3:
>   * Rebased on top of Tom Lendacky's protected guest
>     changes (https://lore.kernel.org/patchwork/cover/1468760/)
> 
> Changes since v1:
>   * Fixed format issues in commit log.
> 
>   arch/x86/include/asm/pgtable.h |  4 ++++
>   arch/x86/mm/ioremap.c          |  8 ++++++--
>   include/linux/cc_platform.h    | 13 +++++++++++++
>   3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 448cd01eb3ec..ecefccbdf2e3 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -21,6 +21,10 @@
>   #define pgprot_encrypted(prot)	__pgprot(__sme_set(pgprot_val(prot)))
>   #define pgprot_decrypted(prot)	__pgprot(__sme_clr(pgprot_val(prot)))
>   
> +/* Make the page accesable by VMM for confidential guests */
> +#define pgprot_cc_guest(prot) __pgprot(pgprot_val(prot) |	\
> +					      tdx_shared_mask())

So this is only for TDX guests, so maybe a name that is less generic.

Alternatively, you could create pgprot_private()/pgprot_shared() functions 
that check for SME/SEV or TDX and do the proper thing.

Then you can redefine pgprot_encrypted()/pgprot_decrypted() to the new 
functions?

> +
>   #ifndef __ASSEMBLY__
>   #include <asm/x86_init.h>
>   #include <asm/pkru.h>
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 026031b3b782..83daa3f8f39c 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -17,6 +17,7 @@
>   #include <linux/cc_platform.h>
>   #include <linux/efi.h>
>   #include <linux/pgtable.h>
> +#include <linux/cc_platform.h>
>   
>   #include <asm/set_memory.h>
>   #include <asm/e820/api.h>
> @@ -26,6 +27,7 @@
>   #include <asm/pgalloc.h>
>   #include <asm/memtype.h>
>   #include <asm/setup.h>
> +#include <asm/tdx.h>
>   
>   #include "physaddr.h"
>   
> @@ -87,8 +89,8 @@ static unsigned int __ioremap_check_ram(struct resource *res)
>   }
>   
>   /*
> - * In a SEV guest, NONE and RESERVED should not be mapped encrypted because
> - * there the whole memory is already encrypted.
> + * In a SEV or TDX guest, NONE and RESERVED should not be mapped encrypted (or
> + * private in TDX case) because there the whole memory is already encrypted.
>    */
>   static unsigned int __ioremap_check_encrypted(struct resource *res)
>   {
> @@ -246,6 +248,8 @@ __ioremap_caller(resource_size_t phys_addr, unsigned long size,
>   	prot = PAGE_KERNEL_IO;
>   	if ((io_desc.flags & IORES_MAP_ENCRYPTED) || encrypted)
>   		prot = pgprot_encrypted(prot);
> +	else if (cc_platform_has(CC_ATTR_GUEST_SHARED_MAPPING_INIT))
> +		prot = pgprot_cc_guest(prot);

And if you do the new functions this could be:

	if ((io_desc.flags & IORES_MAP_ENCRYPTED) || encrypted)
		prot = pgprot_private(prot);
	else
		prot = pgprot_shared(prot);

Thanks,
Tom

>   
>   	switch (pcm) {
>   	case _PAGE_CACHE_MODE_UC:
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index 7728574d7783..edb1d7a2f6af 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -81,6 +81,19 @@ enum cc_attr {
>   	 * Examples include TDX Guest.
>   	 */
>   	CC_ATTR_GUEST_UNROLL_STRING_IO,
> +
> +	/**
> +	 * @CC_ATTR_GUEST_SHARED_MAPPING_INIT: IO Remapped memory is marked
> +	 *				       as shared.
> +	 *
> +	 * The platform/OS is running as a guest/virtual machine and
> +	 * initializes all IO remapped memory as shared.
> +	 *
> +	 * Examples include TDX Guest (SEV marks all pages as shared by default
> +	 * so this feature cannot be enabled for it).
> +	 */
> +	CC_ATTR_GUEST_SHARED_MAPPING_INIT,
> +
>   };
>   
>   #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
>