linux-kernel - [PATCH 3/3] habanalabs: prevent device PTE read/write during hard-reset

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Date:   Sat,  6 Apr 2019 15:45:11 +0300
From:   Oded Gabbay <oded.gabbay@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     gregkh@...uxfoundation.org
Subject: [PATCH 3/3] habanalabs: prevent device PTE read/write during hard-reset

During hard-reset, contexts are closed as part of the tear-down process.
After a context is closed, the driver cleans up the page tables of that
context in the device's DRAM. This action is both dangerous and
unnecessary.

It is unnecessary, because the device is going through a hard-reset, which
means the device's DRAM contents are no longer valid and the device's MMU
is being reset.

It is dangerous, because if the hard-reset came as a result of a PCI
freeze, this action may cause the entire host machine to hang.

Therefore, prevent all device PTE updates when a hard-reset operation is
pending.

Signed-off-by: Oded Gabbay <oded.gabbay@...il.com>
---
 drivers/misc/habanalabs/goya/goya.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/misc/habanalabs/goya/goya.c b/drivers/misc/habanalabs/goya/goya.c
index 2bef21bcbe1e..bde11fc2c251 100644
--- a/drivers/misc/habanalabs/goya/goya.c
+++ b/drivers/misc/habanalabs/goya/goya.c
@@ -4057,6 +4057,9 @@ static u64 goya_read_pte(struct hl_device *hdev, u64 addr)
 {
 	struct goya_device *goya = hdev->asic_specific;

+	if (hdev->hard_reset_pending)
+		return U64_MAX;
+
 	return readq(hdev->pcie_bar[DDR_BAR_ID] +
 			(addr - goya->ddr_bar_cur_addr));
 }
@@ -4065,6 +4068,9 @@ static void goya_write_pte(struct hl_device *hdev, u64 addr, u64 val)
 {
 	struct goya_device *goya = hdev->asic_specific;

+	if (hdev->hard_reset_pending)
+		return;
+
 	writeq(val, hdev->pcie_bar[DDR_BAR_ID] +
 			(addr - goya->ddr_bar_cur_addr));
 }
-- 
2.17.1