Re: [PATCHv5 10/12] x86/tdx: Unaccepted memory support

[Borislav Petkov <bp@alien8.de>]

On Mon, Apr 25, 2022 at 06:39:32AM +0300, Kirill A. Shutemov wrote:
> Subject: [PATCHv5 10/12] x86/tdx: Unaccepted memory support

Patch subject needs a verb:

"Add ... "

> All preparations are complete.

Drop this sentence.

> Hookup TDX-specific code to accept memory.
> 
> Accepting the memory is the same process as converting memory from
> shared to private: kernel notifies VMM with MAP_GPA hypercall and then
> accept pages with ACCEPT_PAGE module call.
> 
> The implementation in core kernel uses tdx_enc_status_changed(). It
> already used for converting memory to shared and back for I/O
> transactions.
> 
> Boot stub provides own implementation of tdx_accept_memory(). It is
> similar in structure to tdx_enc_status_changed(), but only cares about
> converting memory to private.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  arch/x86/Kconfig                  |  1 +
>  arch/x86/boot/compressed/mem.c    | 24 ++++++++-
>  arch/x86/boot/compressed/tdx.c    | 85 +++++++++++++++++++++++++++++++
>  arch/x86/coco/tdx/tdx.c           | 31 +++++++----
>  arch/x86/include/asm/shared/tdx.h |  2 +
>  arch/x86/mm/unaccepted_memory.c   |  9 +++-
>  6 files changed, 141 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 7021ec725dd3..e4c31dbea6d7 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -885,6 +885,7 @@ config INTEL_TDX_GUEST
>  	select ARCH_HAS_CC_PLATFORM
>  	select X86_MEM_ENCRYPT
>  	select X86_MCE
> +	select UNACCEPTED_MEMORY

WARNING: unmet direct dependencies detected for UNACCEPTED_MEMORY
  Depends on [n]: EFI [=y] && EFI_STUB [=y] && !KEXEC_CORE [=y]
  Selected by [y]:
  - INTEL_TDX_GUEST [=y] && HYPERVISOR_GUEST [=y] && X86_64 [=y] && CPU_SUP_INTEL [=y] && X86_X2APIC [=y]

WARNING: unmet direct dependencies detected for UNACCEPTED_MEMORY
  Depends on [n]: EFI [=y] && EFI_STUB [=y] && !KEXEC_CORE [=y]
  Selected by [y]:
  - INTEL_TDX_GUEST [=y] && HYPERVISOR_GUEST [=y] && X86_64 [=y] && CPU_SUP_INTEL [=y] && X86_X2APIC [=y]


> diff --git a/arch/x86/boot/compressed/mem.c b/arch/x86/boot/compressed/mem.c
> index b5058c975d26..539fff27de49 100644
> --- a/arch/x86/boot/compressed/mem.c
> +++ b/arch/x86/boot/compressed/mem.c
> @@ -5,6 +5,8 @@
>  #include "error.h"
>  #include "find.h"
>  #include "math.h"
> +#include "tdx.h"
> +#include <asm/shared/tdx.h>
>  
>  #define PMD_SHIFT	21
>  #define PMD_SIZE	(_AC(1, UL) << PMD_SHIFT)
> @@ -12,10 +14,30 @@
>  
>  extern struct boot_params *boot_params;
>  
> +static bool is_tdx_guest(void)

There is arch/x86/boot/compressed/tdx.c which already looks at that leaf
and detects crap. Why is that hastily slapped here too?

> +{
> +	static bool once;
> +	static bool is_tdx;
> +
> +	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;
> +}
> +
>  static inline void __accept_memory(phys_addr_t start, phys_addr_t end)
>  {
>  	/* Platform-specific memory-acceptance call goes here */
> -	error("Cannot accept memory");
> +	if (is_tdx_guest())
> +		tdx_accept_memory(start, end);
> +	else
> +		error("Cannot accept memory");

What is that supposed to catch?

> diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
> index 918a7606f53c..57fd2bf28484 100644
> --- a/arch/x86/boot/compressed/tdx.c
> +++ b/arch/x86/boot/compressed/tdx.c
> @@ -3,12 +3,14 @@
>  #include "../cpuflags.h"
>  #include "../string.h"
>  #include "../io.h"
> +#include "align.h"
>  #include "error.h"
>  
>  #include <vdso/limits.h>
>  #include <uapi/asm/vmx.h>
>  
>  #include <asm/shared/tdx.h>
> +#include <asm/page_types.h>
>  
>  /* Called from __tdx_hypercall() for unrecoverable failure */
>  void __tdx_hypercall_failed(void)
> @@ -75,3 +77,86 @@ void early_tdx_detect(void)
>  	pio_ops.f_outb = tdx_outb;
>  	pio_ops.f_outw = tdx_outw;
>  }
> +
> +enum pg_level {
> +	PG_LEVEL_4K,
> +	PG_LEVEL_2M,
> +	PG_LEVEL_1G,
> +};
> +
> +#define PTE_SHIFT 9

At least stick those in a header.

> +static bool try_accept_one(phys_addr_t *start, unsigned long len,
> +			  enum pg_level pg_level)

No need to break that line.

Also, it doesn't need to be bool - you can simply return accept_size on
success and 0 on error so that you don't have an I/O argument.

Ditto for the copy in coco/tdx/tdx.c

> +{
> +	unsigned long accept_size = PAGE_SIZE << (pg_level * PTE_SHIFT);
> +	u64 tdcall_rcx;
> +	u8 page_size;
> +
> +	if (!IS_ALIGNED(*start, accept_size))
> +		return false;
> +
> +	if (len < accept_size)
> +		return false;
> +
> +	/*
> +	 * 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 false;
> +	}
> +
> +	tdcall_rcx = *start | page_size;
> +	if (__tdx_module_call(TDX_ACCEPT_PAGE, tdcall_rcx, 0, 0, 0, NULL))
> +		return false;
> +
> +	*start += accept_size;
> +	return true;
> +}
> +
> +void tdx_accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	/*
> +	 * Notify the VMM about page mapping conversion. More info about ABI
> +	 * can be found in TDX Guest-Host-Communication Interface (GHCI),
> +	 * section "TDG.VP.VMCALL<MapGPA>"
> +	 */
> +	if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
> +		error("Accepting memory failed\n");
> +	/*
> +	 * For shared->private conversion, accept the page using
> +	 * TDX_ACCEPT_PAGE TDX module call.
> +	 */
> +	while (start < end) {
> +		unsigned long len = end - start;
> +
> +		/*
> +		 * Try larger accepts first. It gives chance to VMM to keep
> +		 * 1G/2M SEPT entries where possible and speeds up process by

"SEPT"?

> +		 * cutting number of hypercalls (if successful).
> +		 */
> +
> +		if (try_accept_one(&start, len, PG_LEVEL_1G))
> +			continue;
> +
> +		if (try_accept_one(&start, len, PG_LEVEL_2M))
> +			continue;
> +
> +		if (!try_accept_one(&start, len, PG_LEVEL_4K))
> +			error("Accepting memory failed\n");
> +	}
> +}
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index ddb60a87b426..ab4deb897942 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -580,16 +580,9 @@ static bool try_accept_one(phys_addr_t *start, unsigned long len,
>  	return true;
>  }
>  
> -/*
> - * 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
> - * of the page in response.
> - */
> -static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
> +static bool tdx_enc_status_changed_phys(phys_addr_t start, phys_addr_t end,

Why? is tdx_enc_status_changed_virt() coming too?

> +					bool enc)
>  {
> -	phys_addr_t start = __pa(vaddr);
> -	phys_addr_t end   = __pa(vaddr + numpages * PAGE_SIZE);
> -
>  	if (!enc) {
>  		/* Set the shared (decrypted) bits: */
>  		start |= cc_mkdec(0);
> @@ -634,6 +627,25 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
>  	return true;
>  }
>  
> +void tdx_accept_memory(phys_addr_t start, phys_addr_t end)
> +{
> +	if (!tdx_enc_status_changed_phys(start, end, true))
> +		panic("Accepting memory failed\n");
> +}
> +
> +/*
> + * 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
> + * of the page in response.
> + */
> +static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
> +{
> +	phys_addr_t start = __pa(vaddr);
> +	phys_addr_t end = __pa(vaddr + numpages * PAGE_SIZE);
> +
> +	return tdx_enc_status_changed_phys(start, end, enc);
> +}
> +
>  void __init tdx_early_init(void)
>  {
>  	u64 cc_mask;
> @@ -645,6 +657,7 @@ void __init tdx_early_init(void)
>  		return;
>  
>  	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> +	setup_clear_cpu_cap(X86_FEATURE_MCE);

What, no comment? Why does TDX need to disable MCE?

>  	cc_set_vendor(CC_VENDOR_INTEL);
>  	cc_mask = get_cc_mask();
> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> index 956ced04c3be..97534c334473 100644
> --- a/arch/x86/include/asm/shared/tdx.h
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -81,5 +81,7 @@ struct tdx_module_output {
>  u64 __tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
>  		      struct tdx_module_output *out);
>  
> +void tdx_accept_memory(phys_addr_t start, phys_addr_t end);
> +
>  #endif /* !__ASSEMBLY__ */
>  #endif /* _ASM_X86_SHARED_TDX_H */
> diff --git a/arch/x86/mm/unaccepted_memory.c b/arch/x86/mm/unaccepted_memory.c
> index 1327f64d5205..de0790af1824 100644
> --- a/arch/x86/mm/unaccepted_memory.c
> +++ b/arch/x86/mm/unaccepted_memory.c
> @@ -6,6 +6,7 @@
>  
>  #include <asm/io.h>
>  #include <asm/setup.h>
> +#include <asm/shared/tdx.h>
>  #include <asm/unaccepted_memory.h>
>  
>  /* Protects unaccepted memory bitmap */
> @@ -29,7 +30,13 @@ void accept_memory(phys_addr_t start, phys_addr_t end)
>  		unsigned long len = range_end - range_start;
>  
>  		/* Platform-specific memory-acceptance call goes here */
> -		panic("Cannot accept memory");
> +		if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
> +			tdx_accept_memory(range_start * PMD_SIZE,
> +					  range_end * PMD_SIZE);
> +		} else {
> +			panic("Cannot accept memory");

Why panic here? A WARN_ONCE() should suffice, methinks.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette