Re: [Patch v3 02/14] x86/ioapic: Gate decrypted mapping on cc_platform_has() attribute

[Sathyanarayanan Kuppuswamy]

On 11/16/22 10:41 AM, Michael Kelley wrote:
> Current code always maps the IOAPIC as shared (decrypted) in a
> confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
> enabled use a paravisor running in VMPL0 to emulate the IOAPIC.
> In such a case, the IOAPIC must be accessed as private (encrypted).
> 
> Fix this by gating the IOAPIC decrypted mapping on a new
> cc_platform_has() attribute that a subsequent patch in the series
> will set only for Hyper-V guests.
> 
> Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Reviewed-by: Wei Liu <wei.liu@xxxxxxxxxx>
> ---

Looks fine to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>

>  arch/x86/kernel/apic/io_apic.c |  3 ++-
>  include/linux/cc_platform.h    | 12 ++++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index a868b76..c65e0cc 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2686,7 +2686,8 @@ static void io_apic_set_fixmap(enum fixed_addresses idx, phys_addr_t phys)
>  	 * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot
>  	 * bits, just like normal ioremap():
>  	 */
> -	flags = pgprot_decrypted(flags);
> +	if (!cc_platform_has(CC_ATTR_EMULATED_IOAPIC))
> +		flags = pgprot_decrypted(flags);
>  
>  	__set_fixmap(idx, phys, flags);
>  }
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index cb0d6cd..7a0da75 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -90,6 +90,18 @@ enum cc_attr {
>  	 * Examples include TDX Guest.
>  	 */
>  	CC_ATTR_HOTPLUG_DISABLED,
> +
> +	/**
> +	 * @CC_ATTR_EMULATED_IOAPIC: Guest VM has an emulated I/O APIC
> +	 *
> +	 * The platform/OS is running as a guest/virtual machine with
> +	 * an I/O APIC that is emulated by a paravisor running in the
> +	 * guest VM context. As such, the I/O APIC is accessed in the
> +	 * encrypted portion of the guest physical address space.
> +	 *
> +	 * Examples include Hyper-V SEV-SNP guests using vTOM.
> +	 */
> +	CC_ATTR_EMULATED_IOAPIC,
>  };
>  
>  #ifdef CONFIG_ARCH_HAS_CC_PLATFORM

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer