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    Subject[PATCH 23/26] x86/tdx: ioapic: Add shared bit for IOAPIC base address
    Date
    From: Isaku Yamahata <isaku.yamahata@intel.com>

    The kernel interacts with each bare-metal IOAPIC with a special
    MMIO page. When running under KVM, the guest's IOAPICs are
    emulated by KVM.

    When running as a TDX guest, the guest needs to mark each IOAPIC
    mapping as "shared" with the host. This ensures that TDX private
    protections are not applied to the page, which allows the TDX host
    emulation to work.

    Earlier patches in this series modified ioremap() so that
    ioremap()-created mappings such as virtio will be marked as
    shared. However, the IOAPIC code does not use ioremap() and instead
    uses the fixmap mechanism.

    Introduce a special fixmap helper just for the IOAPIC code. Ensure
    that it marks IOAPIC pages as "shared". This replaces
    set_fixmap_nocache() with __set_fixmap() since __set_fixmap()
    allows custom 'prot' values.

    Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
    Reviewed-by: Andi Kleen <ak@linux.intel.com>
    Reviewed-by: Tony Luck <tony.luck@intel.com>
    Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    arch/x86/kernel/apic/io_apic.c | 18 ++++++++++++++++--
    1 file changed, 16 insertions(+), 2 deletions(-)

    diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
    index c1bb384935b0..d2fef5893e41 100644
    --- a/arch/x86/kernel/apic/io_apic.c
    +++ b/arch/x86/kernel/apic/io_apic.c
    @@ -49,6 +49,7 @@
    #include <linux/slab.h>
    #include <linux/memblock.h>
    #include <linux/msi.h>
    +#include <linux/cc_platform.h>

    #include <asm/irqdomain.h>
    #include <asm/io.h>
    @@ -65,6 +66,7 @@
    #include <asm/irq_remapping.h>
    #include <asm/hw_irq.h>
    #include <asm/apic.h>
    +#include <asm/pgtable.h>

    #define for_each_ioapic(idx) \
    for ((idx) = 0; (idx) < nr_ioapics; (idx)++)
    @@ -2677,6 +2679,18 @@ static struct resource * __init ioapic_setup_resources(void)
    return res;
    }

    +static void io_apic_set_fixmap_nocache(enum fixed_addresses idx,
    + phys_addr_t phys)
    +{
    + pgprot_t flags = FIXMAP_PAGE_NOCACHE;
    +
    + /* Set TDX guest shared bit in pgprot flags */
    + if (cc_platform_has(CC_ATTR_GUEST_TDX))
    + flags = pgprot_decrypted(flags);
    +
    + __set_fixmap(idx, phys, flags);
    +}
    +
    void __init io_apic_init_mappings(void)
    {
    unsigned long ioapic_phys, idx = FIX_IO_APIC_BASE_0;
    @@ -2709,7 +2723,7 @@ void __init io_apic_init_mappings(void)
    __func__, PAGE_SIZE, PAGE_SIZE);
    ioapic_phys = __pa(ioapic_phys);
    }
    - set_fixmap_nocache(idx, ioapic_phys);
    + io_apic_set_fixmap_nocache(idx, ioapic_phys);
    apic_printk(APIC_VERBOSE, "mapped IOAPIC to %08lx (%08lx)\n",
    __fix_to_virt(idx) + (ioapic_phys & ~PAGE_MASK),
    ioapic_phys);
    @@ -2838,7 +2852,7 @@ int mp_register_ioapic(int id, u32 address, u32 gsi_base,
    ioapics[idx].mp_config.flags = MPC_APIC_USABLE;
    ioapics[idx].mp_config.apicaddr = address;

    - set_fixmap_nocache(FIX_IO_APIC_BASE_0 + idx, address);
    + io_apic_set_fixmap_nocache(FIX_IO_APIC_BASE_0 + idx, address);
    if (bad_ioapic_register(idx)) {
    clear_fixmap(FIX_IO_APIC_BASE_0 + idx);
    return -ENODEV;
    --
    2.32.0
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