Re: [PATCH v3] drm/i915: Clearing the Memory Space Enable bit when disabling i915

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Jan 20, 2026 at 04:42:03AM +0000, Jia Yao wrote:
> In a kexec reboot scenario, the GPU's Global Graphics Translation Table
> (GGTT) retains its previous state after the kernel is reloaded, until i915
> reinitializes the GGTT.
> 
> The simple-framebuffer driver is initialized before i915 and accesses the
> PCIe memory space (GPU aperture) through outdated GGTT entries. This leads
> to invalid physical memory accesses, causing GPF or data corruption.
> 
> To prevent such issues, the Memory Space Enable (MSE) bit in the PCI Command
> Register is cleared during i915_driver_shutdown. This disables all PCIe
> memory space access (including MMIO and aperture) at the hardware level.
> After the kernel is reloaded, access to the PCIe memory space will be
> forbidden until i915 is re-initialized.

Still looks like a hack. I think the correct fix would involve
preventing the kexec'd kernel from initializing the fb driver that
is doing the invalid memory accesses.

> 
> Since disabling PCIe memory space affects all MMIO operations, PXP shutdown
> needs to be completed before this point. Calls intel_pxp_fini() before
> disabling memory space to ensure PXP cleanup can still access MMIO registers.
> 
> v2:
>   - follow brace style
> 
> v3:
>   - revise description
> 
> Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14598
> Cc: Alex Zuo <alex.zuo@intel.com>
> Cc: Shuicheng Lin <shuicheng.lin@intel.com>
> Cc: Askar Safin <safinaskar@gmail.com>
> Cc: Pingfan Liu <piliu@redhat.com>
> Suggested-by: Chris Wilson <chris.p.wilson@linux.intel.com>
> Signed-off-by: Jia Yao <jia.yao@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_driver.c | 35 +++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
> index b46cb54ef5dc..766f85726b67 100644
> --- a/drivers/gpu/drm/i915/i915_driver.c
> +++ b/drivers/gpu/drm/i915/i915_driver.c
> @@ -118,6 +118,33 @@
>  
>  static const struct drm_driver i915_drm_driver;
>  
> +static int i915_enable_device(struct pci_dev *pdev)
> +{
> +	u32 cmd;
> +	int ret;
> +
> +	ret = pci_enable_device(pdev);
> +	if (ret)
> +		return ret;
> +
> +	pci_read_config_dword(pdev, PCI_COMMAND, &cmd);
> +	if (!(cmd & PCI_COMMAND_MEMORY))
> +		pci_write_config_dword(pdev, PCI_COMMAND, cmd | PCI_COMMAND_MEMORY);
> +
> +	return 0;
> +}
> +
> +static void i915_disable_device(struct pci_dev *pdev)
> +{
> +	u32 cmd;
> +
> +	pci_read_config_dword(pdev, PCI_COMMAND, &cmd);
> +	if (cmd & PCI_COMMAND_MEMORY)
> +		pci_write_config_dword(pdev, PCI_COMMAND, cmd & ~PCI_COMMAND_MEMORY);
> +
> +	pci_disable_device(pdev);
> +}
> +
>  static int i915_workqueues_init(struct drm_i915_private *dev_priv)
>  {
>  	/*
> @@ -788,7 +815,7 @@ int i915_driver_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  	struct intel_display *display;
>  	int ret;
>  
> -	ret = pci_enable_device(pdev);
> +	ret = i915_enable_device(pdev);
>  	if (ret) {
>  		pr_err("Failed to enable graphics device: %pe\n", ERR_PTR(ret));
>  		return ret;
> @@ -796,7 +823,7 @@ int i915_driver_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  
>  	i915 = i915_driver_create(pdev, ent);
>  	if (IS_ERR(i915)) {
> -		pci_disable_device(pdev);
> +		i915_disable_device(pdev);
>  		return PTR_ERR(i915);
>  	}
>  
> @@ -885,7 +912,7 @@ int i915_driver_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
>  	enable_rpm_wakeref_asserts(&i915->runtime_pm);
>  	i915_driver_late_release(i915);
>  out_pci_disable:
> -	pci_disable_device(pdev);
> +	i915_disable_device(pdev);
>  	i915_probe_error(i915, "Device initialization failed (%d)\n", ret);
>  	return ret;
>  }
> @@ -1003,6 +1030,7 @@ void i915_driver_shutdown(struct drm_i915_private *i915)
>  
>  	intel_dmc_suspend(display);
>  
> +	intel_pxp_fini(i915);
>  	i915_gem_suspend(i915);
>  
>  	/*
> @@ -1020,6 +1048,7 @@ void i915_driver_shutdown(struct drm_i915_private *i915)
>  	enable_rpm_wakeref_asserts(&i915->runtime_pm);
>  
>  	intel_runtime_pm_driver_last_release(&i915->runtime_pm);
> +	i915_disable_device(to_pci_dev(i915->drm.dev));
>  }
>  
>  static bool suspend_to_idle(struct drm_i915_private *dev_priv)
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel