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

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