Re: [PATCH v11 6/9] s390/pci: Store PCI error information for passthrough devices

[Farhan Ali <alifm@linux.ibm.com>]

On 3/25/2026 10:01 AM, Alex Williamson wrote:
> On Mon, 16 Mar 2026 12:15:41 -0700
> Farhan Ali <alifm@linux.ibm.com> wrote:
>
>> For a passthrough device we need co-operation from user space to recover
>> the device. This would require to bubble up any error information to user
>> space.  Let's store this error information for passthrough devices, so it
>> can be retrieved later.
>>
>> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
>> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
>> ---
>>   arch/s390/include/asm/pci.h      | 28 ++++++++++
>>   arch/s390/pci/pci.c              |  1 +
>>   arch/s390/pci/pci_event.c        | 94 +++++++++++++++++++-------------
>>   drivers/vfio/pci/vfio_pci_zdev.c |  2 +
>>   4 files changed, 87 insertions(+), 38 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
>> index ec8a772bf526..383f6483b656 100644
>> --- a/arch/s390/include/asm/pci.h
>> +++ b/arch/s390/include/asm/pci.h
>> @@ -118,6 +118,31 @@ struct zpci_bus {
>>   	enum pci_bus_speed	max_bus_speed;
>>   };
>>   
>> +/* Content Code Description for PCI Function Error */
>> +struct zpci_ccdf_err {
>> +	u32 reserved1;
>> +	u32 fh;                         /* function handle */
>> +	u32 fid;                        /* function id */
>> +	u32 ett         :  4;           /* expected table type */
>> +	u32 mvn         : 12;           /* MSI vector number */
>> +	u32 dmaas       :  8;           /* DMA address space */
>> +	u32 reserved2   :  6;
>> +	u32 q           :  1;           /* event qualifier */
>> +	u32 rw          :  1;           /* read/write */
>> +	u64 faddr;                      /* failing address */
>> +	u32 reserved3;
>> +	u16 reserved4;
>> +	u16 pec;                        /* PCI event code */
>> +} __packed;
>> +
>> +#define ZPCI_ERR_PENDING_MAX 4
>> +struct zpci_ccdf_pending {
>> +	u8 count;
>> +	u8 head;
>> +	u8 tail;
>> +	struct zpci_ccdf_err err[ZPCI_ERR_PENDING_MAX];
>> +};
>> +
>>   /* Private data per function */
>>   struct zpci_dev {
>>   	struct zpci_bus *zbus;
>> @@ -193,6 +218,8 @@ struct zpci_dev {
>>   	struct iommu_domain *s390_domain; /* attached IOMMU domain */
>>   	struct kvm_zdev *kzdev;
>>   	struct mutex kzdev_lock;
>> +	struct zpci_ccdf_pending pending_errs;
>> +	struct mutex pending_errs_lock;
>>   	spinlock_t dom_lock;		/* protect s390_domain change */
>>   };
>>   
>> @@ -331,6 +358,7 @@ void zpci_debug_exit_device(struct zpci_dev *);
>>   int zpci_report_error(struct pci_dev *, struct zpci_report_error_header *);
>>   int zpci_clear_error_state(struct zpci_dev *zdev);
>>   int zpci_reset_load_store_blocked(struct zpci_dev *zdev);
>> +void zpci_cleanup_pending_errors(struct zpci_dev *zdev);
>>   
>>   #ifdef CONFIG_NUMA
>>   
>> diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
>> index 87077e510266..bc253cc52056 100644
>> --- a/arch/s390/pci/pci.c
>> +++ b/arch/s390/pci/pci.c
>> @@ -915,6 +915,7 @@ struct zpci_dev *zpci_create_device(u32 fid, u32 fh, enum zpci_state state)
>>   	mutex_init(&zdev->state_lock);
>>   	mutex_init(&zdev->fmb_lock);
>>   	mutex_init(&zdev->kzdev_lock);
>> +	mutex_init(&zdev->pending_errs_lock);
>>   
>>   	return zdev;
>>   
>> diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c
>> index de504925f709..5b24f3a9fe23 100644
>> --- a/arch/s390/pci/pci_event.c
>> +++ b/arch/s390/pci/pci_event.c
>> @@ -17,23 +17,6 @@
>>   #include "pci_bus.h"
>>   #include "pci_report.h"
>>   
>> -/* Content Code Description for PCI Function Error */
>> -struct zpci_ccdf_err {
>> -	u32 reserved1;
>> -	u32 fh;				/* function handle */
>> -	u32 fid;			/* function id */
>> -	u32 ett		:  4;		/* expected table type */
>> -	u32 mvn		: 12;		/* MSI vector number */
>> -	u32 dmaas	:  8;		/* DMA address space */
>> -	u32		:  6;
>> -	u32 q		:  1;		/* event qualifier */
>> -	u32 rw		:  1;		/* read/write */
>> -	u64 faddr;			/* failing address */
>> -	u32 reserved3;
>> -	u16 reserved4;
>> -	u16 pec;			/* PCI event code */
>> -} __packed;
>> -
>>   /* Content Code Description for PCI Function Availability */
>>   struct zpci_ccdf_avail {
>>   	u32 reserved1;
>> @@ -75,6 +58,41 @@ static bool is_driver_supported(struct pci_driver *driver)
>>   	return true;
>>   }
>>   
>> +static void zpci_store_pci_error(struct pci_dev *pdev,
>> +				 struct zpci_ccdf_err *ccdf)
>> +{
>> +	struct zpci_dev *zdev = to_zpci(pdev);
>> +	int i;
>> +
>> +	mutex_lock(&zdev->pending_errs_lock);
>> +	if (zdev->pending_errs.count >= ZPCI_ERR_PENDING_MAX) {
>> +		pr_err("%s: Maximum number (%d) of pending error events queued",
>> +		       pci_name(pdev), ZPCI_ERR_PENDING_MAX);
>> +		mutex_unlock(&zdev->pending_errs_lock);
>> +		return;
>> +	}
>> +
>> +	i = zdev->pending_errs.tail % ZPCI_ERR_PENDING_MAX;
>> +	memcpy(&zdev->pending_errs.err[i], ccdf, sizeof(struct zpci_ccdf_err));
>> +	zdev->pending_errs.tail++;
>> +	zdev->pending_errs.count++;
>> +	mutex_unlock(&zdev->pending_errs_lock);
>> +}
>> +
>> +void zpci_cleanup_pending_errors(struct zpci_dev *zdev)
>> +{
>> +	struct pci_dev *pdev = NULL;
>> +
>> +	guard(mutex)(&zdev->pending_errs_lock);
>> +	pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);
>> +	if (zdev->pending_errs.count)
>> +		pr_info("%s: Unhandled PCI error events count=%d",
>> +			pci_name(pdev), zdev->pending_errs.count);
>> +	memset(&zdev->pending_errs, 0, sizeof(struct zpci_ccdf_pending));
>> +	pci_dev_put(pdev);
>> +}
>> +EXPORT_SYMBOL_GPL(zpci_cleanup_pending_errors);
>> +
>>   static pci_ers_result_t zpci_event_notify_error_detected(struct pci_dev *pdev,
>>   							 struct pci_driver *driver)
>>   {
>> @@ -169,7 +187,8 @@ static pci_ers_result_t zpci_event_do_reset(struct pci_dev *pdev,
>>    * and the platform determines which functions are affected for
>>    * multi-function devices.
>>    */
>> -static pci_ers_result_t zpci_event_attempt_error_recovery(struct pci_dev *pdev)
>> +static pci_ers_result_t zpci_event_attempt_error_recovery(struct pci_dev *pdev,
>> +							  struct zpci_ccdf_err *ccdf)
>>   {
>>   	pci_ers_result_t ers_res = PCI_ERS_RESULT_DISCONNECT;
>>   	struct zpci_dev *zdev = to_zpci(pdev);
>> @@ -188,13 +207,6 @@ static pci_ers_result_t zpci_event_attempt_error_recovery(struct pci_dev *pdev)
>>   	}
>>   	pdev->error_state = pci_channel_io_frozen;
>>   
>> -	if (needs_mediated_recovery(pdev)) {
>> -		pr_info("%s: Cannot be recovered in the host because it is a pass-through device\n",
>> -			pci_name(pdev));
>> -		status_str = "failed (pass-through)";
>> -		goto out_unlock;
>> -	}
>> -
>>   	driver = to_pci_driver(pdev->dev.driver);
>>   	if (!is_driver_supported(driver)) {
>>   		if (!driver) {
>> @@ -210,12 +222,23 @@ static pci_ers_result_t zpci_event_attempt_error_recovery(struct pci_dev *pdev)
>>   		goto out_unlock;
>>   	}
>>   
>> +	if (needs_mediated_recovery(pdev))
>> +		zpci_store_pci_error(pdev, ccdf);
>> +
>>   	ers_res = zpci_event_notify_error_detected(pdev, driver);
>>   	if (ers_result_indicates_abort(ers_res)) {
>>   		status_str = "failed (abort on detection)";
>>   		goto out_unlock;
>>   	}
>>   
>> +	if (needs_mediated_recovery(pdev)) {
>> +		pr_info("%s: Leaving recovery of pass-through device to user-space\n",
>> +			pci_name(pdev));
>> +		ers_res = PCI_ERS_RESULT_RECOVERED;
>> +		status_str = "in progress";
>> +		goto out_unlock;
>> +	}
>> +
>>   	if (ers_res != PCI_ERS_RESULT_NEED_RESET) {
>>   		ers_res = zpci_event_do_error_state_clear(pdev, driver);
>>   		if (ers_result_indicates_abort(ers_res)) {
>> @@ -260,25 +283,20 @@ static pci_ers_result_t zpci_event_attempt_error_recovery(struct pci_dev *pdev)
>>    * @pdev: PCI function for which to report
>>    * @es: PCI channel failure state to report
>>    */
>> -static void zpci_event_io_failure(struct pci_dev *pdev, pci_channel_state_t es)
>> +static void zpci_event_io_failure(struct pci_dev *pdev, pci_channel_state_t es,
>> +				  struct zpci_ccdf_err *ccdf)
>>   {
>>   	struct pci_driver *driver;
>>   
>>   	pci_dev_lock(pdev);
>>   	pdev->error_state = es;
>> -	/**
>> -	 * While vfio-pci's error_detected callback notifies user-space QEMU
>> -	 * reacts to this by freezing the guest. In an s390 environment PCI
>> -	 * errors are rarely fatal so this is overkill. Instead in the future
>> -	 * we will inject the error event and let the guest recover the device
>> -	 * itself.
>> -	 */
>> +
>>   	if (needs_mediated_recovery(pdev))
>> -		goto out;
>> +		zpci_store_pci_error(pdev, ccdf);
>>   	driver = to_pci_driver(pdev->dev.driver);
>>   	if (driver && driver->err_handler && driver->err_handler->error_detected)
>>   		driver->err_handler->error_detected(pdev, pdev->error_state);
>> -out:
>> +
>>   	pci_dev_unlock(pdev);
>>   }
>>   
>> @@ -324,12 +342,12 @@ static void __zpci_event_error(struct zpci_ccdf_err *ccdf)
>>   		break;
>>   	case 0x0040: /* Service Action or Error Recovery Failed */
>>   	case 0x003b:
>> -		zpci_event_io_failure(pdev, pci_channel_io_perm_failure);
>> +		zpci_event_io_failure(pdev, pci_channel_io_perm_failure, ccdf);
>>   		break;
>>   	default: /* PCI function left in the error state attempt to recover */
>> -		ers_res = zpci_event_attempt_error_recovery(pdev);
>> +		ers_res = zpci_event_attempt_error_recovery(pdev, ccdf);
>>   		if (ers_res != PCI_ERS_RESULT_RECOVERED)
>> -			zpci_event_io_failure(pdev, pci_channel_io_perm_failure);
>> +			zpci_event_io_failure(pdev, pci_channel_io_perm_failure, ccdf);
>>   		break;
>>   	}
>>   	pci_dev_put(pdev);
>> diff --git a/drivers/vfio/pci/vfio_pci_zdev.c b/drivers/vfio/pci/vfio_pci_zdev.c
>> index a7bc23ce8483..2be37eab9279 100644
>> --- a/drivers/vfio/pci/vfio_pci_zdev.c
>> +++ b/drivers/vfio/pci/vfio_pci_zdev.c
>> @@ -168,6 +168,8 @@ void vfio_pci_zdev_close_device(struct vfio_pci_core_device *vdev)
>>   
>>   	zdev->mediated_recovery = false;
>>   
>> +	zpci_cleanup_pending_errors(zdev);
>> +
>>   	if (!vdev->vdev.kvm)
>>   		return;
>>   
> It begins to look here like the mediated_recovery should be protected
> by pending_errs_lock and perhaps there should be
> zpci_{start,stop}_mediated_recovery() where we set and clear the flag
> under mutex, while also clearing pending errors in the latter case.
> The various needs_mediated_recovery tests could be pulled in to test
> under mutex as well.  Thanks,
>
> Alex

Thanks Alex for taking a look at the patches. I agree having the 
mediated_recovery flag being protected by the mutex will be a better 
approach. Will add the interfaces you suggested.

Thanks

Farhan