On Thu, Oct 20, 2022 at 10:57:05AM -0700, 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. The new attribute is named
> somewhat generically because similar paravisor emulation cases
> may arise in the future.
>
> Signed-off-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Reviewed-by: Wei Liu <wei.liu@xxxxxxxxxx>
> ---
> arch/x86/kernel/apic/io_apic.c | 3 ++-
> include/linux/cc_platform.h | 13 +++++++++++++
> 2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index a868b76..d2c1bf7 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_HAS_PARAVISOR))
> + 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..b6c4a79 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -90,6 +90,19 @@ enum cc_attr {
> * Examples include TDX Guest.
> */
> CC_ATTR_HOTPLUG_DISABLED,
> +
> + /**
> + * @CC_ATTR_HAS_PARAVISOR: Guest VM is running with a paravisor
> + *
> + * The platform/OS is running as a guest/virtual machine with
> + * a paravisor in VMPL0. Having a paravisor affects things
> + * like whether the I/O APIC is emulated and operates in the
> + * encrypted or decrypted portion of the guest physical address
> + * space.
> + *
> + * Examples include Hyper-V SEV-SNP guests using vTOM.
> + */
> + CC_ATTR_HAS_PARAVISOR,
> };
>
> #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
> --
> 1.8.3.1
>
