Re: [Patch v4 01/13] x86/ioapic: Gate decrypted mapping on cc_platform_has() attribute

Sathyanarayanan Kuppuswamy
2022-12-06T19:27:18Z

On 12/1/22 7:30 PM, Michael Kelley wrote:
> Current code always maps the IO-APIC 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 IO-APIC.
> In such a case, the IO-APIC must be accessed as private (encrypted).
>
> Fix this by gating the IO-APIC decrypted mapping on a new
> cc_platform_has() attribute that a subsequent patch in the series
> will set only for guests using vTOM.
>
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> Reviewed-by: Wei Liu <wei.liu@kernel.org>
> ---

Looks good to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

> 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..2b70e2e 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_ACCESS_IOAPIC_ENCRYPTED))
> + 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..7b63a7d 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_ACCESS_IOAPIC_ENCRYPTED: Guest VM IO-APIC is encrypted
> + *
> + * The platform/OS is running as a guest/virtual machine with
> + * an IO-APIC that is emulated by a paravisor running in the
> + * guest VM context. As such, the IO-APIC is accessed in the
> + * encrypted portion of the guest physical address space.
> + *
> + * Examples include Hyper-V SEV-SNP guests using vTOM.
> + */
> + CC_ATTR_ACCESS_IOAPIC_ENCRYPTED,
> };
>
> #ifdef CONFIG_ARCH_HAS_CC_PLATFORM

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer