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

Borislav Petkov
2022-05-05T10:13:11Z

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.