From: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>
To: linux-coco@lists.linux.dev
Cc: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>,
Ackerley Tng <ackerleytng@google.com>,
Alex Williamson <alex@shazbot.org>,
David Woodhouse <dwmw2@infradead.org>,
David Hildenbrand <david@kernel.org>,
Jason Gunthorpe <jgg@nvidia.com>,
"Joerg Roedel (AMD)" <joro@8bytes.org>,
Kevin Tian <kevin.tian@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Robin Murphy <robin.murphy@arm.com>,
Sean Christopherson <seanjc@google.com>,
Alexey Kardashevskiy <aik@amd.com>,
Xu Yilun <yilun.xu@linux.intel.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Steven Price <steven.price@arm.com>,
Fred Griffoul <griffoul@gmail.com>,
iommu@lists.linux.dev, kvm@vger.kernel.org,
patches@lists.linux.dev
Subject: [RFC PATCH v4 17/25] vfio/pci: Check low-power requests before updating device state
Date: Wed, 4 Nov 2026 20:33:14 +0530 [thread overview]
Message-ID: <20261104150322.3516320-18-aneesh.kumar@kernel.org> (raw)
In-Reply-To: <20261104150322.3516320-1-aneesh.kumar@kernel.org>
In vfio_pm_config_write(), check requests for D1, D2 or D3hot before
vfio_default_config_write() updates vconfig. Return -EBUSY if
vfio_pci_bar_state_change_allowed() returns false. D0 requests and
writes to unrelated PMCSR fields retain their existing handling.
Use vfio_pci_begin_bar_state_change() for D3hot transitions in
vfio_lock_and_set_power_state(), and return its error to the config
write caller. On success, retain the existing behavior
In vfio_pci_runtime_pm_entry(), reject explicit low-power entry before
removing BAR mappings or dropping the runtime-PM reference.
These checks currently allow all requests. Later patches reject
low-power requests while the device supplies guest_memfd backing,
because entering a lower power state can make mapped BAR PFNs
inaccessible.
Cc: Alex Williamson <alex@shazbot.org>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
drivers/vfio/pci/vfio_pci_config.c | 30 ++++++++++++++++++++++++++----
drivers/vfio/pci/vfio_pci_core.c | 30 +++++++++++++++++-------------
drivers/vfio/pci/vfio_pci_priv.h | 1 -
3 files changed, 43 insertions(+), 18 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_config.c b/drivers/vfio/pci/vfio_pci_config.c
index 537e7f8bc884..014f865c1eaf 100644
--- a/drivers/vfio/pci/vfio_pci_config.c
+++ b/drivers/vfio/pci/vfio_pci_config.c
@@ -755,11 +755,15 @@ static bool vfio_af_flr_requested(int offset, __le32 val)
* It takes all the required locks to protect the access of power related
* variables and then invokes vfio_pci_set_power_state().
*/
-static void vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
+static int vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
pci_power_t state)
{
+ int ret;
+
if (state >= PCI_D3hot) {
- vfio_pci_zap_and_down_write_memory_lock(vdev);
+ ret = vfio_pci_begin_bar_state_change(vdev);
+ if (ret)
+ return ret;
vfio_pci_dma_buf_move(vdev, true);
} else {
down_write(&vdev->memory_lock);
@@ -768,19 +772,34 @@ static void vfio_lock_and_set_power_state(struct vfio_pci_core_device *vdev,
vfio_pci_set_power_state(vdev, state);
if (__vfio_pci_memory_enabled(vdev))
vfio_pci_dma_buf_move(vdev, false);
- up_write(&vdev->memory_lock);
+ if (state >= PCI_D3hot)
+ vfio_pci_end_bar_state_change(vdev);
+ else
+ up_write(&vdev->memory_lock);
+ return 0;
+}
+
+static bool vfio_pm_low_power_requested(int offset, __le32 val)
+{
+ return offset == PCI_PM_CTRL &&
+ (le32_to_cpu(val) & PCI_PM_CTRL_STATE_MASK);
}
static int vfio_pm_config_write(struct vfio_pci_core_device *vdev, int pos,
int count, struct perm_bits *perm,
int offset, __le32 val)
{
+ if (vfio_pm_low_power_requested(offset, val) &&
+ !vfio_pci_bar_state_change_allowed(vdev))
+ return -EBUSY;
+
count = vfio_default_config_write(vdev, pos, count, perm, offset, val);
if (count < 0)
return count;
if (offset == PCI_PM_CTRL) {
pci_power_t state;
+ int ret;
switch (le32_to_cpu(val) & PCI_PM_CTRL_STATE_MASK) {
case 0:
@@ -797,7 +816,10 @@ static int vfio_pm_config_write(struct vfio_pci_core_device *vdev, int pos,
break;
}
- vfio_lock_and_set_power_state(vdev, state);
+ ret = vfio_lock_and_set_power_state(vdev, state);
+
+ if (ret)
+ return ret;
}
return count;
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index f31fbd980f3e..6612728a21a4 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -373,24 +373,30 @@ int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev, pci_power_t stat
static int vfio_pci_runtime_pm_entry(struct vfio_pci_core_device *vdev,
struct eventfd_ctx *efdctx)
{
+ int ret;
+
/*
* The vdev power related flags are protected with 'memory_lock'
* semaphore.
*/
- vfio_pci_zap_and_down_write_memory_lock(vdev);
+ ret = vfio_pci_begin_bar_state_change(vdev);
+ if (ret)
+ return ret;
vfio_pci_dma_buf_move(vdev, true);
if (vdev->pm_runtime_engaged) {
- up_write(&vdev->memory_lock);
- return -EINVAL;
+ ret = -EINVAL;
+ goto out_unlock;
}
- vdev->pm_runtime_engaged = true;
+ WRITE_ONCE(vdev->pm_runtime_engaged, true);
vdev->pm_wake_eventfd_ctx = efdctx;
pm_runtime_put_noidle(&vdev->pdev->dev);
- up_write(&vdev->memory_lock);
+ ret = 0;
- return 0;
+out_unlock:
+ vfio_pci_end_bar_state_change(vdev);
+ return ret;
}
static int vfio_pci_core_pm_entry(struct vfio_pci_core_device *vdev, u32 flags,
@@ -445,7 +451,11 @@ static int vfio_pci_core_pm_entry_with_wakeup(
static void __vfio_pci_runtime_pm_exit(struct vfio_pci_core_device *vdev)
{
if (vdev->pm_runtime_engaged) {
- vdev->pm_runtime_engaged = false;
+ /*
+ * Guest_memfd provider setup reads this flag with READ_ONCE()
+ * without memory_lock; runtime resume can clear it concurrently.
+ */
+ WRITE_ONCE(vdev->pm_runtime_engaged, false);
pm_runtime_get_noresume(&vdev->pdev->dev);
if (vdev->pm_wake_eventfd_ctx) {
@@ -1705,12 +1715,6 @@ static void vfio_pci_zap_bars(struct vfio_pci_core_device *vdev)
unmap_mapping_range(core_vdev->inode->i_mapping, start, len, true);
}
-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev)
-{
- down_write(&vdev->memory_lock);
- vfio_pci_zap_bars(vdev);
-}
-
int vfio_pci_begin_bar_state_change(struct vfio_pci_core_device *vdev)
{
if (!vfio_pci_bar_state_change_allowed(vdev))
diff --git a/drivers/vfio/pci/vfio_pci_priv.h b/drivers/vfio/pci/vfio_pci_priv.h
index 0af93f6d9a8a..f7b3178cc890 100644
--- a/drivers/vfio/pci/vfio_pci_priv.h
+++ b/drivers/vfio/pci/vfio_pci_priv.h
@@ -75,7 +75,6 @@ void vfio_config_free(struct vfio_pci_core_device *vdev);
int vfio_pci_set_power_state(struct vfio_pci_core_device *vdev,
pci_power_t state);
-void vfio_pci_zap_and_down_write_memory_lock(struct vfio_pci_core_device *vdev);
/* Success retains memory_lock through the hardware operation. */
int vfio_pci_begin_bar_state_change(struct vfio_pci_core_device *vdev);
void vfio_pci_end_bar_state_change(struct vfio_pci_core_device *vdev);
--
2.43.0
next prev parent reply other threads:[~2026-11-04 15:05 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-04 15:02 [RFC PATCH v4 00/25] KVM/VFIO: Add guest_memfd support for device MMIO Aneesh Kumar K.V (Arm)
2026-11-04 15:02 ` [RFC PATCH v4 01/25] KVM: guest_memfd: Let providers prepare memory regions Aneesh Kumar K.V (Arm)
2026-11-04 15:02 ` [RFC PATCH v4 02/25] KVM: guest_memfd: Dispatch conversion through backing operations Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 03/25] KVM: guest_memfd: Let providers coordinate mapping changes Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 04/25] KVM: guest_memfd: Dispatch revocation through backing operations Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 05/25] KVM: guest_memfd: Split population by backing type Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 06/25] KVM: guest_memfd: Support device-backed PFN providers Aneesh Kumar K.V (Arm)
2026-11-04 18:37 ` Fred Griffoul
2026-11-04 15:03 ` [RFC PATCH v4 07/25] KVM: guest_memfd: Support private/shared conversion of device memory Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 08/25] KVM: guest_memfd: Track private device ranges after attribute updates Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 09/25] KVM: guest_memfd: Support range revocation of device mappings Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 10/25] KVM: guest_memfd: Add shared device mmap through PFN providers Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 11/25] KVM: guest_memfd: Clear private device state on final close Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 12/25] KVM: guest_memfd: Invalidate mappings before memslot unbind Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 13/25] vfio: Track device use by guest_memfd Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 14/25] vfio/pci: Add helpers to check and serialize BAR state changes Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 15/25] vfio/pci: Check command enable changes before updating device state Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 16/25] vfio/pci: Check whether BAR state changes are allowed before reset Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` Aneesh Kumar K.V (Arm) [this message]
2026-11-04 15:03 ` [RFC PATCH v4 18/25] vfio/pci: Track userspace BAR mappings Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 19/25] vfio/pci: Restrict host BAR access for guest_memfd providers Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 20/25] vfio: Dispatch guest_memfd provider operations through the device file Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 21/25] vfio: Serialize guest_memfd attachment with device file operations Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 22/25] vfio/pci: Require D0 before providing guest_memfd BAR backing Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 23/25] iommufd: Support MMIO provider attachment to vDEVICEs Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 24/25] vfio/pci: Add a guest_memfd resource provider for MMIO BARs Aneesh Kumar K.V (Arm)
2026-11-04 15:03 ` [RFC PATCH v4 25/25] KVM: Document device-backed guest_memfd and VFIO usage Aneesh Kumar K.V (Arm)
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