Messages in this thread | | | Subject | Re: [RFC v2 29/32] x86/tdx: Add helper to do MapGPA TDVMALL | From | "Kuppuswamy, Sathyanarayanan" <> | Date | Thu, 20 May 2021 16:14:31 -0700 |
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On 5/19/21 8:59 AM, Dave Hansen wrote: > On 4/26/21 11:01 AM, Kuppuswamy Sathyanarayanan wrote: >> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> >> >> MapGPA TDVMCALL requests the host VMM to map a GPA range as private or >> shared memory mappings. Shared GPA mappings can be used for >> communication beteen TD guest and host VMM, for example for >> paravirtualized IO. > > As usual, I hate the changelog. This appears to just be regurgitating > the spec. > > Is this just for part of converting an existing mapping between private > and shared? If so, please say that. >
How about following change?
x86/tdx: Add helper to do MapGPA hypercall
MapGPA hypercall is used by TDX guests to request VMM convert the existing mapping of given GPA address range between private/shared.
tdx_hcall_gpa_intent() is the wrapper used for making MapGPA hypercall.
>> The new helper tdx_map_gpa() provides access to the operation. > > <sigh> You got your own name wrong. It's tdg_map_gpa() in the patch.
I can use tdx_hcall_gpa_intent().
> > BTW, I agree with Sean on this one: "tdg" is a horrible prefix. You > just proved Sean's point by mistyping it. *EVERYONE* is going to rpeat > that mistake: tdg -> tdx. > >> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h >> index dc80cf7f7d08..4789798d7737 100644 >> --- a/arch/x86/include/asm/tdx.h >> +++ b/arch/x86/include/asm/tdx.h >> @@ -7,6 +7,11 @@ >> >> #ifndef __ASSEMBLY__ >> >> +enum tdx_map_type { >> + TDX_MAP_PRIVATE, >> + TDX_MAP_SHARED, >> +}; > > I like the enum, but please call out that this is a software construct, > not a part of any hardware or VMM ABI. > >> #ifdef CONFIG_INTEL_TDX_GUEST >> >> #include <asm/cpufeature.h> >> @@ -112,6 +117,8 @@ unsigned short tdg_inw(unsigned short port); >> unsigned int tdg_inl(unsigned short port); >> >> extern phys_addr_t tdg_shared_mask(void); >> +extern int tdg_map_gpa(phys_addr_t gpa, int numpages, >> + enum tdx_map_type map_type); >> >> #else // !CONFIG_INTEL_TDX_GUEST >> >> @@ -155,6 +162,12 @@ static inline phys_addr_t tdg_shared_mask(void) >> { >> return 0; >> } >> + >> +static inline int tdg_map_gpa(phys_addr_t gpa, int numpages, >> + enum tdx_map_type map_type) >> +{ >> + return -ENODEV; >> +} > > FWIW, you could probably get away with just inlining tdg_map_gpa(): > > static inline int tdg_map_gpa(phys_addr_t gpa, int numpages, ... > { > u64 ret; > > if (!IS_ENABLED(CONFIG_INTEL_TDX_GUEST)) > return -ENODEV; > > if (map_type == TDX_MAP_SHARED) > gpa |= tdg_shared_mask(); > > ret = tdvmcall(TDVMCALL_MAP_GPA, gpa, ... > > return ret ? -EIO : 0; > } > > Then you don't have three copies of the function signature that can get > out of sync.
I agree that this simplifies the function definition. But, there are other TDX hypercalls definitions in tdx.c. I can't move all of them to the header file. If possible, I would like to group all hypercalls in the same place.
Also, IMO, it is better to hide hypercall internal implementation details in C file. For example, user of MapGPA hypercall does not care about the TDVMCALL_MAP_GPA leaf id value. If we inline this function we have to move such details to header file.
> >> #endif /* CONFIG_INTEL_TDX_GUEST */ >> #endif /* __ASSEMBLY__ */ >> #endif /* _ASM_X86_TDX_H */ >> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c >> index 7e391cd7aa2b..074136473011 100644 >> --- a/arch/x86/kernel/tdx.c >> +++ b/arch/x86/kernel/tdx.c >> @@ -15,6 +15,8 @@ >> #include "tdx-kvm.c" >> #endif >> >> +#define TDVMCALL_MAP_GPA 0x10001 >> + >> static struct { >> unsigned int gpa_width; >> unsigned long attributes; >> @@ -98,6 +100,17 @@ static void tdg_get_info(void) >> physical_mask &= ~tdg_shared_mask(); >> } >> >> +int tdg_map_gpa(phys_addr_t gpa, int numpages, enum tdx_map_type map_type) >> +{ >> + u64 ret; >> + >> + if (map_type == TDX_MAP_SHARED) >> + gpa |= tdg_shared_mask(); >> + >> + ret = tdvmcall(TDVMCALL_MAP_GPA, gpa, PAGE_SIZE * numpages, 0, 0); >> + return ret ? -EIO : 0; >> +} > > The naming Intel chose here is nasty. This doesn't "map" anything. It > modifies an existing mapping from what I can tell. We could name it > much better than the spec, perhaps: > > tdx_hcall_gpa_intent()
I will use this function name in next version.
> > BTW, all of these hypercalls need a consistent prefix.
I can include _hcall in other hypercall helper functions as well.
> > It also needs a comment: > > /* > * 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. > * > * Note: shared->private conversions require further guest > * action to accept the page. > */ > > The intent here is important. It makes it clear that this function > really only plays a role in the conversion process.
Thanks. I will include it in next version.
>
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
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