Currently, iommu_init_ga() checks and disables IOMMU VAPIC support
(i.e. AMD AVIC support in IOMMU) when GAMSup feature bit is not set.
However it forgets to clear IRQ_POSTING_CAP from the previously set
amd_iommu_irq_ops.capability.

This triggers an invalid page fault bug during guest VM warm reboot
if AVIC is enabled since the irq_remapping_cap(IRQ_POSTING_CAP) is
incorrectly set, and crash the system with the following kernel trace.

    BUG: unable to handle page fault for address: 0000000000400dd8
    RIP: 0010:amd_iommu_deactivate_guest_mode+0x19/0xbc
    Call Trace:
     svm_set_pi_irte_mode+0x8a/0xc0 [kvm_amd]
     ? kvm_make_all_cpus_request_except+0x50/0x70 [kvm]
     kvm_request_apicv_update+0x10c/0x150 [kvm]
     svm_toggle_avic_for_irq_window+0x52/0x90 [kvm_amd]
     svm_enable_irq_window+0x26/0xa0 [kvm_amd]
     vcpu_enter_guest+0xbbe/0x1560 [kvm]
     ? avic_vcpu_load+0xd5/0x120 [kvm_amd]
     ? kvm_arch_vcpu_load+0x76/0x240 [kvm]
     ? svm_get_segment_base+0xa/0x10 [kvm_amd]
     kvm_arch_vcpu_ioctl_run+0x103/0x590 [kvm]
     kvm_vcpu_ioctl+0x22a/0x5d0 [kvm]
     __x64_sys_ioctl+0x84/0xc0
     do_syscall_64+0x33/0x40
     entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixes by moving the initializing of AMD IOMMU interrupt remapping mode
(amd_iommu_guest_ir) earlier before setting up the
amd_iommu_irq_ops.capability with appropriate IRQ_POSTING_CAP flag.

[joro:	Squashed the two patches and limited
	check_features_on_all_iommus() to CONFIG_IRQ_REMAP
	to fix a compile warning.]
Signed-off-by: Wei Huang <wei.huang2@amd.com>
Co-developed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20210820202957.187572-2-suravee.suthikulpanit@amd.com
Link: https://lore.kernel.org/r/20210820202957.187572-3-suravee.suthikulpanit@amd.com
Fixes: 8bda0cfb ("iommu/amd: Detect and initialize guest vAPIC log")
Signed-off-by: Joerg Roedel <jroedel@suse.de>