linux-kernel - Re: [RFT PATCH v3 05/21] x86/sev: Move GHCB page based HV communication out of startup code

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Message-ID: <CAMj1kXEikRCP4TyNWWQh7wKErr9YKAe3cCbPw8XMuXLVkr2S_g@mail.gmail.com>
Date: Tue, 20 May 2025 13:49:35 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	linux-efi@...r.kernel.org, x86@...nel.org, Ingo Molnar <mingo@...nel.org>, 
	Dionna Amalie Glaze <dionnaglaze@...gle.com>, Kevin Loughlin <kevinloughlin@...gle.com>, 
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [RFT PATCH v3 05/21] x86/sev: Move GHCB page based HV
 communication out of startup code

On Tue, 20 May 2025 at 13:39, Borislav Petkov <bp@...en8.de> wrote:
>
> On Mon, May 12, 2025 at 09:08:40PM +0200, Ard Biesheuvel wrote:
> > diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> > index f50a606be4f1..07081bb85331 100644
> > --- a/arch/x86/include/asm/sev.h
> > +++ b/arch/x86/include/asm/sev.h
> > @@ -485,6 +485,7 @@ static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
> >  struct snp_guest_request_ioctl;
> >
> >  void setup_ghcb(void);
> > +void snp_register_ghcb_early(unsigned long paddr);
> >  void early_snp_set_memory_private(unsigned long vaddr, unsigned long paddr,
> >                                 unsigned long npages);
> >  void early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
> > @@ -521,8 +522,6 @@ static __always_inline void vc_ghcb_invalidate(struct ghcb *ghcb)
> >       __builtin_memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
> >  }
> >
> > -void vc_forward_exception(struct es_em_ctxt *ctxt);
> > -
> >  /* I/O parameters for CPUID-related helpers */
> >  struct cpuid_leaf {
> >       u32 fn;
> > @@ -533,15 +532,71 @@ struct cpuid_leaf {
> >       u32 edx;
> >  };
> >
> > +int svsm_perform_msr_protocol(struct svsm_call *call);
> >  int snp_cpuid(void (*cpuid_hv)(void *ctx, struct cpuid_leaf *),
> >             void *ctx, struct cpuid_leaf *leaf);
> >
> > +/*
> > + * Issue a VMGEXIT to call the SVSM:
> > + *   - Load the SVSM register state (RAX, RCX, RDX, R8 and R9)
> > + *   - Set the CA call pending field to 1
> > + *   - Issue VMGEXIT
> > + *   - Save the SVSM return register state (RAX, RCX, RDX, R8 and R9)
> > + *   - Perform atomic exchange of the CA call pending field
> > + *
> > + *   - See the "Secure VM Service Module for SEV-SNP Guests" specification for
> > + *     details on the calling convention.
> > + *     - The calling convention loosely follows the Microsoft X64 calling
> > + *       convention by putting arguments in RCX, RDX, R8 and R9.
> > + *     - RAX specifies the SVSM protocol/callid as input and the return code
> > + *       as output.
> > + */
> > +static __always_inline void svsm_issue_call(struct svsm_call *call, u8 *pending)
>
> Why in a header?
>
> At least in sev-internal.h or so.
>
> I'd prefer for this to be in a .c file, though.
>

OK. In that case, it will be implemented in the startup code then, and
exported to the rest of the core kernel via a PIC alias.