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

Kirill A. Shutemov
2022-05-06T20:42:47Z

On Thu, May 05, 2022 at 12:12:52PM +0200, Borislav Petkov wrote:
> 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]

Ughh. Any ideas how to get around it? (Except for implementing kexec
support right away?)
>
>
> > 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?

I'm not happhy with this too.

process_unaccepted_memory() called form EFI stub that called before
decompression code.

I'm not sure how to structure code that it makes sense.

Call early_tdx_detect() from efi_main() in libstub/x86-stub.c?
It would require to include tdx.h from decompression code there which is
non-sense.

I would appreciate an idea.

> > +{
> > + 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?

Booting on a platform that uses unaccepted memory, but kernel doesn't not
support it.

> > 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.

So on the calling side it would look like:

accepted = try_accept_one(start, len, PG_LEVEL_1G)
if (accepted) {
start += accepted;
continue;
}

And the similar for other levels. Is it really better?

>
> 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"?

Secure EPT. EPT for private memory in TDX.

> > + * 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?

tdx_enc_status_changed() deals with virtual addresses.

> > + 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?

It doesn't not suppose to be here. Sorry.

>
> > 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.

As I said before, memory accept failure is fatal.

--
Kirill A. Shutemov