Re: [PATCHv13 9/9] x86/tdx: Add unaccepted memory support

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

On 6/1/23 13:25, Kirill A. Shutemov wrote:
> Hookup TDX-specific code to accept memory.
> 
> Accepting the memory is done with ACCEPT_PAGE module call on every page
> in the range. MAP_GPA hypercall is not required as the unaccepted memory
> is considered private already.
> 
> Extract the part of tdx_enc_status_changed() that does memory acceptance
> in a new helper. Move the helper tdx-shared.c. It is going to be used by
> both main kernel and decompressor.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>   arch/x86/Kconfig                         |  2 +
>   arch/x86/boot/compressed/Makefile        |  2 +-
>   arch/x86/boot/compressed/error.c         | 19 +++++++
>   arch/x86/boot/compressed/error.h         |  1 +
>   arch/x86/boot/compressed/mem.c           | 35 +++++++++++-
>   arch/x86/boot/compressed/tdx-shared.c    |  2 +
>   arch/x86/coco/tdx/Makefile               |  2 +-
>   arch/x86/coco/tdx/tdx-shared.c           | 71 ++++++++++++++++++++++++
>   arch/x86/coco/tdx/tdx.c                  | 70 +----------------------
>   arch/x86/include/asm/shared/tdx.h        |  2 +
>   arch/x86/include/asm/unaccepted_memory.h | 24 ++++++++
>   11 files changed, 160 insertions(+), 70 deletions(-)
>   create mode 100644 arch/x86/boot/compressed/tdx-shared.c
>   create mode 100644 arch/x86/coco/tdx/tdx-shared.c
>   create mode 100644 arch/x86/include/asm/unaccepted_memory.h
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 53bab123a8ee..5c72067c06d4 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -884,9 +884,11 @@ config INTEL_TDX_GUEST
>   	bool "Intel TDX (Trust Domain Extensions) - Guest Support"
>   	depends on X86_64 && CPU_SUP_INTEL
>   	depends on X86_X2APIC
> +	depends on EFI_STUB
>   	select ARCH_HAS_CC_PLATFORM
>   	select X86_MEM_ENCRYPT
>   	select X86_MCE
> +	select UNACCEPTED_MEMORY
>   	help
>   	  Support running as a guest under Intel TDX.  Without this support,
>   	  the guest kernel can not boot or run under TDX.
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index cc4978123c30..b13a58021086 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -106,7 +106,7 @@ ifdef CONFIG_X86_64
>   endif
>   
>   vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
> -vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
> +vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o $(obj)/tdx-shared.o
>   vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
>   
>   vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
> diff --git a/arch/x86/boot/compressed/error.c b/arch/x86/boot/compressed/error.c
> index c881878e56d3..5313c5cb2b80 100644
> --- a/arch/x86/boot/compressed/error.c
> +++ b/arch/x86/boot/compressed/error.c
> @@ -22,3 +22,22 @@ void error(char *m)
>   	while (1)
>   		asm("hlt");
>   }
> +
> +/* EFI libstub  provides vsnprintf() */
> +#ifdef CONFIG_EFI_STUB
> +void panic(const char *fmt, ...)
> +{
> +	static char buf[1024];
> +	va_list args;
> +	int len;
> +
> +	va_start(args, fmt);
> +	len = vsnprintf(buf, sizeof(buf), fmt, args);
> +	va_end(args);
> +
> +	if (len && buf[len - 1] == '\n')
> +		buf[len - 1] = '\0';
> +
> +	error(buf);
> +}
> +#endif
> diff --git a/arch/x86/boot/compressed/error.h b/arch/x86/boot/compressed/error.h
> index 1de5821184f1..86fe33b93715 100644
> --- a/arch/x86/boot/compressed/error.h
> +++ b/arch/x86/boot/compressed/error.h
> @@ -6,5 +6,6 @@
>   
>   void warn(char *m);
>   void error(char *m) __noreturn;
> +void panic(const char *fmt, ...) __noreturn __cold;
>   
>   #endif /* BOOT_COMPRESSED_ERROR_H */
> diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
> index 4ecf26576a77..d2b6948a7801 100644
> --- a/arch/x86/boot/compressed/mem.c
> +++ b/arch/x86/boot/compressed/mem.c
> @@ -2,11 +2,44 @@
>   
>   #include "error.h"
>   #include "misc.h"
> +#include "tdx.h"
> +#include <asm/shared/tdx.h>
> +
> +/*
> + * accept_memory() and process_unaccepted_memory() called from EFI stub which
> + * runs before decompresser and its early_tdx_detect().
> + *
> + * Enumerate TDX directly from the early users.
> + */
> +static bool early_is_tdx_guest(void)
> +{
> +	static bool once;
> +	static bool is_tdx;
> +
> +	if (!IS_ENABLED(CONFIG_INTEL_TDX_GUEST))
> +		return false;
> +
> +	if (!once) {
> +		u32 eax, sig[3];
> +
> +		cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax,
> +			    &sig[0], &sig[2],  &sig[1]);
> +		is_tdx = !memcmp(TDX_IDENT, sig, sizeof(sig));
> +		once = true;
> +	}
> +
> +	return is_tdx;
> +}
>   
>   void arch_accept_memory(phys_addr_t start, phys_addr_t end)
>   {
>   	/* Platform-specific memory-acceptance call goes here */
> -	error("Cannot accept memory");
> +	if (early_is_tdx_guest()) {
> +		if (tdx_accept_memory(start, end))
> +			return;
> +	}
> +
> +	error("Cannot accept memory: unknown platform\n");

So this is a change in this version. If tdx_accept_memory() fails, you'll 
report unknown platform. Wouldn't it be better to have an error message 
that indicates a failure in the accept path?

Thanks,
Tom

>   }
>   
>   void init_unaccepted_memory(void)
> diff --git a/arch/x86/boot/compressed/tdx-shared.c b/arch/x86/boot/compressed/tdx-shared.c
> new file mode 100644
> index 000000000000..5ac43762fe13
> --- /dev/null
> +++ b/arch/x86/boot/compressed/tdx-shared.c
> @@ -0,0 +1,2 @@
> +#include "error.h"
> +#include "../../coco/tdx/tdx-shared.c"
> diff --git a/arch/x86/coco/tdx/Makefile b/arch/x86/coco/tdx/Makefile
> index 46c55998557d..2c7dcbf1458b 100644
> --- a/arch/x86/coco/tdx/Makefile
> +++ b/arch/x86/coco/tdx/Makefile
> @@ -1,3 +1,3 @@
>   # SPDX-License-Identifier: GPL-2.0
>   
> -obj-y += tdx.o tdcall.o
> +obj-y += tdx.o tdx-shared.o tdcall.o
> diff --git a/arch/x86/coco/tdx/tdx-shared.c b/arch/x86/coco/tdx/tdx-shared.c
> new file mode 100644
> index 000000000000..ef20ddc37b58
> --- /dev/null
> +++ b/arch/x86/coco/tdx/tdx-shared.c
> @@ -0,0 +1,71 @@
> +#include <asm/tdx.h>
> +#include <asm/pgtable.h>
> +
> +static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
> +				    enum pg_level pg_level)
> +{
> +	unsigned long accept_size = page_level_size(pg_level);
> +	u64 tdcall_rcx;
> +	u8 page_size;
> +
> +	if (!IS_ALIGNED(start, accept_size))
> +		return 0;
> +
> +	if (len < accept_size)
> +		return 0;
> +
> +	/*
> +	 * Pass the page physical address to the TDX module to accept the
> +	 * pending, private page.
> +	 *
> +	 * Bits 2:0 of RCX encode page size: 0 - 4K, 1 - 2M, 2 - 1G.
> +	 */
> +	switch (pg_level) {
> +	case PG_LEVEL_4K:
> +		page_size = 0;
> +		break;
> +	case PG_LEVEL_2M:
> +		page_size = 1;
> +		break;
> +	case PG_LEVEL_1G:
> +		page_size = 2;
> +		break;
> +	default:
> +		return 0;
> +	}
> +
> +	tdcall_rcx = start | page_size;
> +	if (__tdx_module_call(TDX_ACCEPT_PAGE, tdcall_rcx, 0, 0, 0, NULL))
> +		return 0;
> +
> +	return accept_size;
> +}
> +
> +bool tdx_accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	/*
> +	 * For shared->private conversion, accept the page using
> +	 * TDX_ACCEPT_PAGE TDX module call.
> +	 */
> +	while (start < end) {
> +		unsigned long len = end - start;
> +		unsigned long accept_size;
> +
> +		/*
> +		 * Try larger accepts first. It gives chance to VMM to keep
> +		 * 1G/2M Secure EPT entries where possible and speeds up
> +		 * process by cutting number of hypercalls (if successful).
> +		 */
> +
> +		accept_size = try_accept_one(start, len, PG_LEVEL_1G);
> +		if (!accept_size)
> +			accept_size = try_accept_one(start, len, PG_LEVEL_2M);
> +		if (!accept_size)
> +			accept_size = try_accept_one(start, len, PG_LEVEL_4K);
> +		if (!accept_size)
> +			return false;
> +		start += accept_size;
> +	}
> +
> +	return true;
> +}
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index 0d5fe6e24e45..a9c4ba6c5c5d 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -713,46 +713,6 @@ static bool tdx_cache_flush_required(void)
>   	return true;
>   }
>   
> -static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
> -				    enum pg_level pg_level)
> -{
> -	unsigned long accept_size = page_level_size(pg_level);
> -	u64 tdcall_rcx;
> -	u8 page_size;
> -
> -	if (!IS_ALIGNED(start, accept_size))
> -		return 0;
> -
> -	if (len < accept_size)
> -		return 0;
> -
> -	/*
> -	 * Pass the page physical address to the TDX module to accept the
> -	 * pending, private page.
> -	 *
> -	 * Bits 2:0 of RCX encode page size: 0 - 4K, 1 - 2M, 2 - 1G.
> -	 */
> -	switch (pg_level) {
> -	case PG_LEVEL_4K:
> -		page_size = 0;
> -		break;
> -	case PG_LEVEL_2M:
> -		page_size = 1;
> -		break;
> -	case PG_LEVEL_1G:
> -		page_size = 2;
> -		break;
> -	default:
> -		return 0;
> -	}
> -
> -	tdcall_rcx = start | page_size;
> -	if (__tdx_module_call(TDX_ACCEPT_PAGE, tdcall_rcx, 0, 0, 0, NULL))
> -		return 0;
> -
> -	return accept_size;
> -}
> -
>   /*
>    * Inform the VMM of the guest's intent for this physical page: shared with
>    * the VMM or private to the guest.  The VMM is expected to change its mapping
> @@ -777,33 +737,9 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
>   	if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
>   		return false;
>   
> -	/* private->shared conversion  requires only MapGPA call */
> -	if (!enc)
> -		return true;
> -
> -	/*
> -	 * For shared->private conversion, accept the page using
> -	 * TDX_ACCEPT_PAGE TDX module call.
> -	 */
> -	while (start < end) {
> -		unsigned long len = end - start;
> -		unsigned long accept_size;
> -
> -		/*
> -		 * Try larger accepts first. It gives chance to VMM to keep
> -		 * 1G/2M Secure EPT entries where possible and speeds up
> -		 * process by cutting number of hypercalls (if successful).
> -		 */
> -
> -		accept_size = try_accept_one(start, len, PG_LEVEL_1G);
> -		if (!accept_size)
> -			accept_size = try_accept_one(start, len, PG_LEVEL_2M);
> -		if (!accept_size)
> -			accept_size = try_accept_one(start, len, PG_LEVEL_4K);
> -		if (!accept_size)
> -			return false;
> -		start += accept_size;
> -	}
> +	/* shared->private conversion requires memory to be accepted before use */
> +	if (enc)
> +		return tdx_accept_memory(start, end);
>   
>   	return true;
>   }
> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> index 1ff0ee822961..19228beb4894 100644
> --- a/arch/x86/include/asm/shared/tdx.h
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -91,5 +91,7 @@ struct tdx_module_output {
>   u64 __tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
>   		      struct tdx_module_output *out);
>   
> +bool tdx_accept_memory(phys_addr_t start, phys_addr_t end);
> +
>   #endif /* !__ASSEMBLY__ */
>   #endif /* _ASM_X86_SHARED_TDX_H */
> diff --git a/arch/x86/include/asm/unaccepted_memory.h b/arch/x86/include/asm/unaccepted_memory.h
> new file mode 100644
> index 000000000000..f0ab217b566f
> --- /dev/null
> +++ b/arch/x86/include/asm/unaccepted_memory.h
> @@ -0,0 +1,24 @@
> +#ifndef _ASM_X86_UNACCEPTED_MEMORY_H
> +#define _ASM_X86_UNACCEPTED_MEMORY_H
> +
> +#include <linux/efi.h>
> +#include <asm/tdx.h>
> +
> +static inline void arch_accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	/* Platform-specific memory-acceptance call goes here */
> +	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
> +		if (tdx_accept_memory(start, end))
> +			return;
> +	}
> +
> +	panic("Cannot accept memory: unknown platform\n");
> +}
> +
> +static inline struct efi_unaccepted_memory *efi_get_unaccepted_table(void)
> +{
> +	if (efi.unaccepted == EFI_INVALID_TABLE_ADDR)
> +		return NULL;
> +	return __va(efi.unaccepted);
> +}
> +#endif