Re: [RFC PATCH] target/i386: restrict SEV to 64 bit host builds

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jun 26, 2024 at 03:03:07PM +0100, Alex Bennée wrote:
> Re-enabling the 32 bit host build on i686 showed the recently merged
> SEV code doesn't take enough care over its types. While the format
> strings could use more portable types there isn't much we can do about
> casting uint64_t into a pointer. The easiest solution seems to be just
> to disable SEV for a 32 bit build. It's highly unlikely anyone would
> want this functionality anyway.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  target/i386/sev.h       | 2 +-
>  target/i386/meson.build | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/target/i386/sev.h b/target/i386/sev.h
> index 858005a119..b0cb9dd7ed 100644
> --- a/target/i386/sev.h
> +++ b/target/i386/sev.h
> @@ -45,7 +45,7 @@ typedef struct SevKernelLoaderContext {
>      size_t cmdline_size;
>  } SevKernelLoaderContext;
>  
> -#ifdef CONFIG_SEV
> +#if defined(CONFIG_SEV) && defined(HOST_X86_64)
>  bool sev_enabled(void);
>  bool sev_es_enabled(void);
>  bool sev_snp_enabled(void);
> diff --git a/target/i386/meson.build b/target/i386/meson.build
> index 075117989b..d2a008926c 100644
> --- a/target/i386/meson.build
> +++ b/target/i386/meson.build
> @@ -6,7 +6,7 @@ i386_ss.add(files(
>    'xsave_helper.c',
>    'cpu-dump.c',
>  ))
> -i386_ss.add(when: 'CONFIG_SEV', if_true: files('host-cpu.c', 'confidential-guest.c'))
> +i386_ss.add(when: ['CONFIG_SEV', 'HOST_X86_64'], if_true: files('host-cpu.c', 'confidential-guest.c'))
>  
>  # x86 cpu type
>  i386_ss.add(when: 'CONFIG_KVM', if_true: files('host-cpu.c'))
> @@ -21,7 +21,7 @@ i386_system_ss.add(files(
>    'cpu-apic.c',
>    'cpu-sysemu.c',
>  ))
> -i386_system_ss.add(when: 'CONFIG_SEV', if_true: files('sev.c'), if_false: files('sev-sysemu-stub.c'))
> +i386_system_ss.add(when: ['CONFIG_SEV', 'HOST_X86_64'], if_true: files('sev.c'), if_false: files('sev-sysemu-stub.c'))
>  
>  i386_user_ss = ss.source_set()

Instead of changing each usage of CONFIG_SEV, is it better to
prevent it getting enabled in the first place ?

eg. move

  #CONFIG_SEV=n

From

  configs/devices/i386-softmmu/default.mak

to

  configs/devices/x86_64-softmmu/default.mak

And then also change

  hw/i386/Kconfig

to say

  config SEV
      bool
      select X86_FW_OVMF
      depends on KVM && X86_64


With regards,
Daniel
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