From: Keith Busch <kbusch@kernel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>,
Nirmal Patel <nirmal.patel@linux.intel.com>,
jonathan.derrick@linux.dev, acelan.kao@canonical.com,
lpieralisi@kernel.org, kw@linux.com, robh@kernel.org,
bhelgaas@google.com, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, kaihengfeng@gmail.com
Subject: Re: [PATCH] PCI: vmd: Delay interrupt handling on MTL VMD controller
Date: Fri, 13 Sep 2024 09:24:29 -0600 [thread overview]
Message-ID: <ZuRZLRFrCjXlrd4w@kbusch-mbp> (raw)
In-Reply-To: <20240913111142.4cgrmirofhhgrbqm@thinkpad>
On Fri, Sep 13, 2024 at 04:41:42PM +0530, Manivannan Sadhasivam wrote:
> I'm not able to understand the bug properly. The erratum indicates that the MSI
> from device reaches the VMD before other writes to the registers. So this is an
> ordering issue as MSI takes precedence over other writes from the device.
>
> So the workaround is to read the device register in the MSI handler to make sure
> the previous writes from the device are flushed. IIUC, once the MSI reaches the
> VMD, it will trigger the IRQ handler in the NVMe driver and in the handler, CQE
> status register is read first up. This flow matches with the workaround
> suggested.
>
> Is any write being performed to the NVMe device before reading any register in
> the MSI handler? Or the current CQE read is not able to satisfy the workaround?
> Please clarify.
The CQE is not a device register. It exists in host memory, so reading
that from the driver isn't going to flush writes from IO devices.
next prev parent reply other threads:[~2024-09-13 15:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-03 2:55 [PATCH] PCI: vmd: Delay interrupt handling on MTL VMD controller Kai-Heng Feng
2024-09-03 4:28 ` Manivannan Sadhasivam
2024-09-03 7:07 ` Kai-Heng Feng
2024-09-03 8:00 ` Manivannan Sadhasivam
2024-09-03 14:51 ` Keith Busch
2024-09-04 1:57 ` Kai-Heng Feng
2024-09-04 6:22 ` Manivannan Sadhasivam
2024-09-06 1:56 ` Kai-Heng Feng
2024-09-12 17:45 ` Nirmal Patel
2024-09-13 5:55 ` Kai-Heng Feng
2024-09-13 11:11 ` Manivannan Sadhasivam
2024-09-13 15:24 ` Keith Busch [this message]
2024-09-13 16:14 ` Manivannan Sadhasivam
2024-09-13 16:34 ` Keith Busch
2024-09-03 15:29 ` Nirmal Patel
2024-09-03 16:17 ` kernel test robot
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