linux-kernel - [PATCH] iommu/amd: Explicitly bail from enable_iommus

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Message-ID: <20250315030928.2373250-1-seanjc@google.com>
Date: Fri, 14 Mar 2025 20:09:28 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Joerg Roedel <joro@...tes.org>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>, Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH] iommu/amd: Explicitly bail from enable_iommus_vapic() when in
 legacy mode

Bail early from enable_iommus_vapic() if IOMMUs are configured for either
of the legacy modes, as it's absurdly difficult to see that
iommu_ga_log_enable() is guaranteed to fail because iommu_init_ga_log()
skips allocating the ga_log.

Opportunistically have iommu_ga_log_enable() WARN if it's called without
IOMMUs being configured to support AVIC/vAPIC.

Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 drivers/iommu/amd/init.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index cb536d372b12..05c568da589a 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -931,8 +931,8 @@ static int iommu_ga_log_enable(struct amd_iommu *iommu)
 
 static int iommu_init_ga_log(struct amd_iommu *iommu)
 {
-	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
-		return 0;
+	if (WARN_ON_ONCE(!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir)))
+		return -EINVAL;
 
 	iommu->ga_log = iommu_alloc_pages(GFP_KERNEL, get_order(GA_LOG_SIZE));
 	if (!iommu->ga_log)
@@ -2863,8 +2863,10 @@ static void enable_iommus_vapic(void)
 			return;
 	}
 
-	if (AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir) &&
-	    !check_feature(FEATURE_GAM_VAPIC)) {
+	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
+		return;
+
+	if (!check_feature(FEATURE_GAM_VAPIC)) {
 		amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA;
 		return;
 	}

base-commit: ea9bd29a9c0d757b3384ae3e633e6bbaddf00725
-- 
2.49.0.rc1.451.g8f38331e32-goog