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    SubjectRe: [RFC v2 10/32] x86/tdx: Wire up KVM hypercalls
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    On 4/26/21 11:01 AM, Kuppuswamy Sathyanarayanan wrote:
    > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    >
    > KVM hypercalls have to be wrapped into vendor-specific TDVMCALLs.

    How about:

    KVM hypercalls use the "vmcall" or "vmmcall" instructions. Although the
    ABI is similar, those instructions no longer function for TDX guests.
    Make TDVMCALLs instead of VMCALL/VMCALL.

    > diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
    > index 338119852512..2fa85481520b 100644
    > --- a/arch/x86/include/asm/kvm_para.h
    > +++ b/arch/x86/include/asm/kvm_para.h
    > @@ -6,6 +6,7 @@
    > #include <asm/alternative.h>
    > #include <linux/interrupt.h>
    > #include <uapi/asm/kvm_para.h>
    > +#include <asm/tdx.h>
    >
    > extern void kvmclock_init(void);
    >
    > @@ -34,6 +35,10 @@ static inline bool kvm_check_and_clear_guest_paused(void)
    > static inline long kvm_hypercall0(unsigned int nr)
    > {
    > long ret;
    > +
    > + if (is_tdx_guest())
    > + return tdx_kvm_hypercall0(nr);

    ... all of these look OK.

    > #endif /* _ASM_X86_TDX_H */
    > diff --git a/arch/x86/kernel/tdcall.S b/arch/x86/kernel/tdcall.S
    > index 81af70c2acbd..964bfd7fc682 100644
    > --- a/arch/x86/kernel/tdcall.S
    > +++ b/arch/x86/kernel/tdcall.S
    > @@ -11,6 +11,7 @@
    > * refer to TDX GHCI specification).
    > */
    > #define TDVMCALL_EXPOSE_REGS_MASK 0xfc00
    > +#define TDVMCALL_VENDOR_KVM 0x4d564b2e584454 /* "TDX.KVM" */
    >
    > /*
    > * TDX guests use the TDCALL instruction to make
    > @@ -198,3 +199,9 @@ SYM_FUNC_START(__tdvmcall)
    > call do_tdvmcall
    > retq
    > SYM_FUNC_END(__tdvmcall)
    > +
    > +SYM_FUNC_START(__tdvmcall_vendor_kvm)
    > + movq $TDVMCALL_VENDOR_KVM, %r10
    > + call do_tdvmcall
    > + retq
    > +SYM_FUNC_END(__tdvmcall_vendor_kvm)

    Granted, this is not a ton of assembly. But, it does look a bit weird.
    It needs a comment and/or a mention in the changelog.

    R10 is not part of the function call ABI, but it is a part of the
    TDVMCALL ABI. This little assembly wrapper lets us reuse do_tdvmcall()
    for both KVM-specific hypercalls TDVMCALL_VENDOR_KVM and the more
    generic __tdvmcalls.

    > --- a/arch/x86/kernel/tdx.c
    > +++ b/arch/x86/kernel/tdx.c
    > @@ -8,6 +8,10 @@
    >
    > #include <linux/cpu.h>
    >
    > +#ifdef CONFIG_KVM_GUEST
    > +#include "tdx-kvm.c"
    > +#endif
    > +
    > static struct {
    > unsigned int gpa_width;
    > unsigned long attributes;

    I know KVM does weird stuff. But, this is *really* weird. Why are we
    #including a .c file into another .c file?

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