Good questions. @Pingfan Liu @Ville Syrjälä Driver-wise, no other access except for pxp stuff, for that after disabling PCI_COMMAND_MEMORY, any access will cause MMIO failure, they will not be able to be hidden. And the invalid access is not from pxp, otherwise just doing intel_pxp_fini in i915_driver_shutdown will fix the issue, it might come from firmware or other that i915 driver can't see.
Current solution is defensive, not harmful just like turning on write protection on a floppy disk when not using it. Thanks, Jia -----Original Message----- From: Ville Syrjälä <[email protected]> Sent: Wednesday, October 8, 2025 9:16 AM To: Yao, Jia <[email protected]> Cc: [email protected]; Zuo, Alex <[email protected]>; Lin, Shuicheng <[email protected]>; Askar Safin <[email protected]>; Pingfan Liu <[email protected]>; Chris Wilson <[email protected]> Subject: Re: [PATCH v2] drm/i915: Setting/clearing the memory access bit when en/disabling i915 On Wed, Oct 08, 2025 at 04:06:39PM +0000, Yao, Jia wrote: > The actual bug is showing in > https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14598 > if CONFIG_INTEL_IOMMU_DEFAULT_ON=y , that IOMMU prevent the invalid access, > but if CONFIG_INTEL_IOMMU_DEFAULT_ON=n, the invalid access will directly > cause system crash after kexec reboot. I was asking you whether that invalid access was caused by that pxp stuff or not? If yes, then just fix it. If not, then I guess someone needs to keep on debugging. > > -----Original Message----- > From: Ville Syrjälä <[email protected]> > Sent: Wednesday, October 8, 2025 5:22 AM > To: Yao, Jia <[email protected]> > Cc: [email protected]; Zuo, Alex <[email protected]>; > Lin, Shuicheng <[email protected]>; Askar Safin > <[email protected]>; Pingfan Liu <[email protected]>; Chris Wilson > <[email protected]> > Subject: Re: [PATCH v2] drm/i915: Setting/clearing the memory access > bit when en/disabling i915 > > On Tue, Oct 07, 2025 at 09:40:45PM +0000, Yao, Jia wrote: > > You mean intel_pxp_fini(i915) ? > > This is because mei_me_shutdown is called after > > i915_driver_shutdown in pci_device_shutdown sequence. If we don't > > close pxp in advance, it will cause > > > > [ 295.584775] i915 0000:00:02.0: [drm] *ERROR* gt: MMIO unreliable > > (forcewake register returns 0xFFFFFFFF)! > > So that is the actual bug you're trying to fix? Please just submit the pxp > fix on its own. > > > > > Since we disabled PCI_COMMAND_MEMORY in i915_driver_shutdown > > > > Thanks, > > Jia > > > > -----Original Message----- > > From: Ville Syrjälä <[email protected]> > > Sent: Tuesday, October 7, 2025 2:25 PM > > To: Yao, Jia <[email protected]> > > Cc: [email protected]; Zuo, Alex <[email protected]>; > > Lin, Shuicheng <[email protected]>; Askar Safin > > <[email protected]>; Pingfan Liu <[email protected]>; Chris Wilson > > <[email protected]> > > Subject: Re: [PATCH v2] drm/i915: Setting/clearing the memory access > > bit when en/disabling i915 > > > > On Tue, Oct 07, 2025 at 08:25:14PM +0000, Jia Yao wrote: > > > Make i915's PCI device management more robust by always > > > setting/clearing the memory access bit when enabling/disabling the > > > device, and by consolidating this logic into helper functions. > > > > > > It fixes kexec reboot issue by disabling memory access before > > > shutting down the device, which can block unsafe and unwanted access from > > > DMA. > > > > > > v2: > > > - follow brace style > > > > > > Link: > > > https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14598 > > > Cc: Alex Zuo <[email protected]> > > > Cc: Shuicheng Lin <[email protected]> > > > Cc: Askar Safin <[email protected]> > > > Cc: Pingfan Liu <[email protected]> > > > Suggested-by: Chris Wilson <[email protected]> > > > Signed-off-by: Jia Yao <[email protected]> > > > --- > > > 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; > > > +} > > > > NAK. If the pci code is broken then fix the problem there. > > Do not add ugly hacks into random drivers. > > > > > + > > > +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); > > > > What is that doing in this patch? > > > > > 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 > > -- > Ville Syrjälä > Intel -- Ville Syrjälä Intel
