linux-kernel - [PATCH 2/3] iommu/amd: Relocate GAMSup check to early_enable

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Date:   Fri, 20 Aug 2021 15:29:56 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org
Cc:     joro@...tes.org, Jon.Grimm@....com, wei.huang2@....com,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH 2/3] iommu/amd: Relocate GAMSup check to early_enable_iommus

From: Wei Huang <wei.huang2@....com>

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.

Signed-off-by: Wei Huang <wei.huang2@....com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 drivers/iommu/amd/init.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index c97961451ac5..ea3330ed545d 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -867,13 +867,6 @@ static int iommu_init_ga(struct amd_iommu *iommu)
 	int ret = 0;
 
 #ifdef CONFIG_IRQ_REMAP
-	/* Note: We have already checked GASup from IVRS table.
-	 *       Now, we need to make sure that GAMSup is set.
-	 */
-	if (AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) &&
-	    !iommu_feature(iommu, FEATURE_GAM_VAPIC))
-		amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA;
-
 	ret = iommu_init_ga_log(iommu);
 #endif /* CONFIG_IRQ_REMAP */
 
@@ -2490,6 +2483,14 @@ static void early_enable_iommus(void)
 	}
 
 #ifdef CONFIG_IRQ_REMAP
+	/*
+	 * Note: We have already checked GASup from IVRS table.
+	 *       Now, we need to make sure that GAMSup is set.
+	 */
+	if (AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) &&
+	    !check_feature_on_all_iommus(FEATURE_GAM_VAPIC))
+		amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA;
+
 	if (AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
 		amd_iommu_irq_ops.capability |= (1 << IRQ_POSTING_CAP);
 #endif
-- 
2.17.1