Re: [edk2-devel] [PATCH RFC v2 04/28] MdePkg: Define the Page State Change VMGEXIT structures

["Laszlo Ersek" <lersek@redhat.com>]

On 05/04/21 16:48, Tom Lendacky wrote:
> 
> 
> On 5/4/21 8:59 AM, Laszlo Ersek wrote:
>> On 05/04/21 14:33, Laszlo Ersek wrote:
>>> On 04/30/21 13:51, Brijesh Singh wrote:
>>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3275&data=04%7C01%7Cthomas.lendacky%40amd.com%7Cf400bca14b6f4f138a1908d90f05090f%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637557336582189771%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=bjXNVWGpurRGUZkjemvDQR%2FYnEQRG9ENN22jUjtkNP0%3D&reserved=0
>>>>
>>>> The Page State Change NAE exit will be used by the SEV-SNP guest to
>>>> request a page state change using the GHCB protocol. See the GHCB
>>>> spec section 4.1.6 and 2.3.1 for more detail on the structure
>>>> definitions.
>>>>
>>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>>> Cc: Min Xu <min.m.xu@intel.com>
>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>> Cc: Erdem Aktas <erdemaktas@google.com>
>>>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>>>> ---
>>>>  MdePkg/Include/Register/Amd/Fam17Msr.h | 15 ++++++++++
>>>>  MdePkg/Include/Register/Amd/Ghcb.h     | 29 ++++++++++++++++++++
>>>>  2 files changed, 44 insertions(+)
>>>>
>>>> diff --git a/MdePkg/Include/Register/Amd/Fam17Msr.h b/MdePkg/Include/Register/Amd/Fam17Msr.h
>>>> index e19bd04b6c..432cee2feb 100644
>>>> --- a/MdePkg/Include/Register/Amd/Fam17Msr.h
>>>> +++ b/MdePkg/Include/Register/Amd/Fam17Msr.h
>>>> @@ -58,6 +58,19 @@ typedef union {
>>>>      UINT64  GuestFrameNumber:52;
>>>>    } GhcbGpaRegister;
>>>>  
>>>> +  struct {
>>>> +    UINT64 Function:12;
>>>> +    UINT64 GuestFrameNumber:40;
>>>> +    UINT64 Operation:4;
>>>> +    UINT64 Reserved:8;
>>>> +  } SnpPageStateChangeRequest;
>>>> +
>>>> +  struct {
>>>> +    UINT32 Function:12;
>>>> +    UINT32 Reserved:20;
>>>> +    UINT32 ErrorCode;
>>>> +  } SnpPageStateChangeResponse;
>>>> +
>>>>    VOID    *Ghcb;
>>>>  
>>> This matches section 2.3.1 in rev 2.00.
>>>
>>>>    UINT64  GhcbPhysicalAddress;
>>>> @@ -69,6 +82,8 @@ typedef union {
>>>>  #define GHCB_INFO_CPUID_RESPONSE           5
>>>>  #define GHCB_INFO_GHCB_GPA_REGISTER_REQUEST   18
>>>>  #define GHCB_INFO_GHCB_GPA_REGISTER_RESPONSE  19
>>>> +#define GHCB_INFO_SNP_PAGE_STATE_CHANGE_REQUEST   20
>>>> +#define GHCB_INFO_SNP_PAGE_STATE_CHANGE_RESPONSE  21
>>>>  #define GHCB_HYPERVISOR_FEATURES_REQUEST   128
>>>>  #define GHCB_HYPERVISOR_FEATURES_RESPONSE  129
>>>>  #define GHCB_INFO_TERMINATE_REQUEST        256
>>>
>>> Matches section 2.3.1.
>>>
>>>> diff --git a/MdePkg/Include/Register/Amd/Ghcb.h b/MdePkg/Include/Register/Amd/Ghcb.h
>>>> index 2d64a4c28f..1e7c0daed3 100644
>>>> --- a/MdePkg/Include/Register/Amd/Ghcb.h
>>>> +++ b/MdePkg/Include/Register/Amd/Ghcb.h
>>>> @@ -54,6 +54,7 @@
>>>>  #define SVM_EXIT_NMI_COMPLETE   0x80000003ULL
>>>>  #define SVM_EXIT_AP_RESET_HOLD  0x80000004ULL
>>>>  #define SVM_EXIT_AP_JUMP_TABLE  0x80000005ULL
>>>> +#define SVM_EXIT_SNP_PAGE_STATE_CHANGE    0x80000010ULL
>>>>  #define SVM_EXIT_HYPERVISOR_FEATURES  0x8000FFFDULL
>>>>  #define SVM_EXIT_UNSUPPORTED    0x8000FFFFULL
>>>>  
>>>
>>> Matches "Table 5. List of Supported Non-Automatic Events".
>>>
>>>> @@ -160,4 +161,32 @@ typedef union {
>>>>  #define GHCB_HV_FEATURES_SNP_AP_CREATE                    (GHCB_HV_FEATURES_SNP | BIT1)
>>>>  #define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION         (GHCB_HV_FEATURES_SNP_AP_CREATE | BIT2)
>>>>  #define GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION_TIMER   (GHCB_HV_FEATURES_SNP_RESTRICTED_INJECTION | BIT3)
>>>> +
>>>> +// SNP Page State Change
>>>
>>> (1) Comment style.
>>>
>>>> +#define SNP_PAGE_STATE_MAX_NPAGES           4095
>>>> +#define SNP_PAGE_STATE_MAX_ENTRY            253
>>>> +#define SNP_PAGE_STATE_PRIVATE              1
>>>> +#define SNP_PAGE_STATE_SHARED               2
>>>> +#define SNP_PAGE_STATE_PSMASH               3
>>>> +#define SNP_PAGE_STATE_UNSMASH              4
>>>
>>> (2) The PSMASH and UNSMASH operations are not documented in the rev 2.00
>>> spec, in the GHCB MSR protocol. That's probably because PSMASH and
>>> UNSMASH can only be defined in terms of 2MB pages, and
>>> GHCB_INFO_SNP_PAGE_STATE_CHANGE_REQUEST is suitable only for individual,
>>> 4KB pages. I think it would be useful to point out somehow here that
>>> PSMASH and UNSMASH are restricted to the GHCB shared area protocol
>>> (perhaps extend the leading comment on this block of macros).
>>>
>>> (3) I don't understand what "MAX_NPAGES" stands for (4095). The rest of
>>> the series never uses the macro, and I can't associate it with anything
>>> from the spec. If the macro is supposed to relate to the 4KB / 2MB page
>>> smashing / splitting, then its replacement text should be 512. Unless
>>> the macro corresponds to a definition in the spec, I think we should
>>> drop it.
>>>
>>>> +
>>>> +typedef PACKED struct {
>>>> +  UINT64  CurrentPage:12;
>>>> +  UINT64  GuestFrameNumber:40;
>>>> +  UINT64  Op:4;
>>>> +  UINT64  PageSize:1;
>>>> +  UINT64  Rsvd: 7;
>>>> +} SNP_PAGE_STATE_ENTRY;
>>>> +
>>>> +typedef PACKED struct {
>>>> +  UINT16 CurrentEntry;
>>>> +  UINT16 EndEntry;
>>>> +  UINT32 Rsvd;
>>>> +} SNP_PAGE_STATE_HEADER;
>>>
>>> (4) We tend to write
>>>
>>> #pragma pack (1)
>>> ...
>>> #pragma pack ()
>>>
>>> rather than PACKED -- but anyway, is packing really necessary? "Natural
>>> alignment" is required in edk2. I'm OK with packing, but I think the
>>> pragma is the preferred form.
>>>
>>> (5) Please spell out both "Rsvd" fields above as "Reserved".
>>>
>>> (6) Stray space character in "Rsvd: 7".
>>>
>>> (7) The field name "Op" is inconsistent with the other field name
>>> "Operation".
>>>
>>> (8) I think there is a bug (typo) in the rev 2.00 spec, in 4.1.6 "SNP
>>> Page State Change": it says
>>>
>>>   ... calculated from the supplied guest physical frame number (GFN) for
>>>   the requested page size (GPA = GFN << 12).
>>>
>>> But, if you can choose 2MB page size in the request, then the (GPA = GFN
>>> << 12) formula is not g
>>
>> Sorry, unfinished sentence: I meant that the formula was not generally
>> correct.
> 
> Actually, for any page size, the GPA for any GFN is GFN << 12.
> 
> For the SNP Page State Change NAE event, it is up to the hypervisor to
> ensure that the GFN/GPA supplied is aligned appropriately for the
> requested page size (see 4.1.6 of the GHCB spec where the page operations
> are defined). A GFN is naturally 4K aligned, so only a 2MB page size needs
> GFN/GPA alignment validation.

Thanks. I guess I was confused by the term "for the requested page size".

> For the SNP Page State Change MSR protocol, only a 4K page size is supported.

Yes, that's clear.

Thanks!
Laszlo