Re: [PATCH v2 3/4] x86/sev: Fix broken SNP support with KVM module built-in

[Sean Christopherson <seanjc@google.com>]

On Fri, Jan 31, 2025, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
> 
> This patch fixes issues with enabling SNP host support and effectively
  ^^^^^^^^^^

> ---
>  arch/x86/include/asm/sev.h |  2 ++
>  arch/x86/virt/svm/sev.c    | 23 +++++++----------------
>  2 files changed, 9 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 5d9685f92e5c..1581246491b5 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -531,6 +531,7 @@ static inline void __init snp_secure_tsc_init(void) { }
>  
>  #ifdef CONFIG_KVM_AMD_SEV
>  bool snp_probe_rmptable_info(void);
> +int snp_rmptable_init(void);
>  int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level);
>  void snp_dump_hva_rmpentry(unsigned long address);
>  int psmash(u64 pfn);
> @@ -541,6 +542,7 @@ void kdump_sev_callback(void);
>  void snp_fixup_e820_tables(void);
>  #else
>  static inline bool snp_probe_rmptable_info(void) { return false; }
> +static inline int snp_rmptable_init(void) { return -ENOSYS; }
>  static inline int snp_lookup_rmpentry(u64 pfn, bool *assigned, int *level) { return -ENODEV; }
>  static inline void snp_dump_hva_rmpentry(unsigned long address) {}
>  static inline int psmash(u64 pfn) { return -ENODEV; }
> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c
> index 1dcc027ec77e..42e74a5a7d78 100644
> --- a/arch/x86/virt/svm/sev.c
> +++ b/arch/x86/virt/svm/sev.c
> @@ -505,19 +505,19 @@ static bool __init setup_rmptable(void)
>   * described in the SNP_INIT_EX firmware command description in the SNP
>   * firmware ABI spec.
>   */
> -static int __init snp_rmptable_init(void)
> +int __init snp_rmptable_init(void)
>  {
>  	unsigned int i;
>  	u64 val;
>  
> -	if (!cc_platform_has(CC_ATTR_HOST_SEV_SNP))
> -		return 0;
> +	if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP)))
> +		return -ENOSYS;
>  
> -	if (!amd_iommu_snp_en)
> -		goto nosnp;
> +	if (WARN_ON_ONCE(!amd_iommu_snp_en))
> +		return -ENOSYS;
>  
>  	if (!setup_rmptable())
> -		goto nosnp;
> +		return -ENOSYS;
>  
>  	/*
>  	 * Check if SEV-SNP is already enabled, this can happen in case of
> @@ -530,7 +530,7 @@ static int __init snp_rmptable_init(void)
>  	/* Zero out the RMP bookkeeping area */
>  	if (!clear_rmptable_bookkeeping()) {
>  		free_rmp_segment_table();
> -		goto nosnp;
> +		return -ENOSYS;
>  	}
>  
>  	/* Zero out the RMP entries */
> @@ -562,17 +562,8 @@ static int __init snp_rmptable_init(void)
>  	crash_kexec_post_notifiers = true;
>  
>  	return 0;
> -
> -nosnp:
> -	cc_platform_clear(CC_ATTR_HOST_SEV_SNP);
> -	return -ENOSYS;
>  }
>  
> -/*
> - * This must be called after the IOMMU has been initialized.
> - */
> -device_initcall(snp_rmptable_init);

There's the wee little problem that snp_rmptable_init() is never called as of
this patch.  Dropping the device_initcall() needs to happen in the same patch
that wires up the IOMMU code to invoke snp_rmptable_init().  At a glance, I don't
see anything in this patch that can reasonably go in before the IOMMU change.