linux-kernel - Re: [PATCH v4 2/4] x86/sev: Change snp_guest_issue_request's fw

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Date:   Thu, 27 Oct 2022 10:09:55 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Dionna Glaze <dionnaglaze@...gle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Tom Lendacky <Thomas.Lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v4 2/4] x86/sev: Change snp_guest_issue_request's fw_err

On Mon, Oct 24, 2022 at 4:47 PM Dionna Glaze <dionnaglaze@...gle.com> wrote:
>
> The GHCB specification declares that the firmware error value for a
> guest request will be stored in the lower 32 bits of EXIT_INFO_2.
> The upper 32 bits are for the VMM's own error code. The fw_err argument
> is thus a misnomer, and callers will need access to all 64 bits.
>
> The type of unsigned long also causes problems, since sw_exit_info2 is
> u64 (unsigned long long) vs the argument's previous unsigned long*.
> The signature change requires the follow-up change to
> drivers/virt/coco/sev-guest to use the new expected type in order to
> compile.
>
> The firmware might not even be called, so we bookend the call with the
> no firmware call error and clearing the error.
>
> Cc: Tom Lendacky <Thomas.Lendacky@....com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Peter Gonda <pgonda@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
>
> Fixes: d5af44dde546 ("x86/sev: Provide support for SNP guest request NAEs")
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
> ---
>  arch/x86/include/asm/sev.h |  4 ++--
>  arch/x86/kernel/sev.c      | 10 ++++++----
>  2 files changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index ebc271bb6d8e..8ebd78b6a57c 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -196,7 +196,7 @@ void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
>  void snp_set_wakeup_secondary_cpu(void);
>  bool snp_init(struct boot_params *bp);
>  void __init __noreturn snp_abort(void);
> -int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err);
> +int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, u64 *exitinfo2);
>  #else
>  static inline void sev_es_ist_enter(struct pt_regs *regs) { }
>  static inline void sev_es_ist_exit(void) { }
> @@ -217,7 +217,7 @@ static inline void snp_set_wakeup_secondary_cpu(void) { }
>  static inline bool snp_init(struct boot_params *bp) { return false; }
>  static inline void snp_abort(void) { }
>  static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input,
> -                                         unsigned long *fw_err)
> +                                         u64 *exitinfo2)
>  {
>         return -ENOTTY;
>  }

In another thread Borislav suggested we edit snp_issue_guest_request()
to take a parameter struct pointer instead of a long list of args.
Should we use the opportunity to do this instead of making this list
longer?