[PATCH v2] nvmet: pci-epf: Always configure BAR0 as 64-bit

[PATCH v2] nvmet: pci-epf: Always configure BAR0 as 64-bit

[Niklas Cassel]

NVMe PCIe Transport Specification 1.1, section 2.1.10, claims that the
BAR0 type is Implementation Specific.

However, in NVMe 1.1, the type is required to be 64-bit.

Thus, to make our PCI EPF work on as many host systems as possible,
always configure the BAR0 type to be 64-bit.

In the rare case that the underlying PCI EPC does not support configuring
BAR0 as 64-bit, the call to pci_epc_set_bar() will fail, and we will
return a failure back to the user.

This should not be a problem, as most PCI EPCs support configuring a BAR
as 64-bit (and those EPCs with .only_64bit set to true in epc_features
only support configuring the BAR as 64-bit).

Tested-by: Damien Le Moal <dlemoal@kernel.org>
Fixes: 0faa0fe6f90e ("nvmet: New NVMe PCI endpoint function target driver")
Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
Changes since v1:
-Added Fixes-tag.
-Picked up tags.

 drivers/nvme/target/pci-epf.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/target/pci-epf.c b/drivers/nvme/target/pci-epf.c
index 0136df45ca275..a24f6549c0d15 100644
--- a/drivers/nvme/target/pci-epf.c
+++ b/drivers/nvme/target/pci-epf.c
@@ -2096,8 +2096,15 @@ static int nvmet_pci_epf_configure_bar(struct nvmet_pci_epf *nvme_epf)
 		return -ENODEV;
 	}
 
-	if (epc_features->bar[BAR_0].only_64bit)
-		epf->bar[BAR_0].flags |= PCI_BASE_ADDRESS_MEM_TYPE_64;
+	/*
+	 * While NVMe PCIe Transport Specification 1.1, section 2.1.10, claims
+	 * that the BAR0 type is Implementation Specific, in NVMe 1.1, the type
+	 * is required to be 64-bit. Thus, for interoperability, always set the
+	 * type to 64-bit. In the rare case that the PCI EPC does not support
+	 * configuring BAR0 as 64-bit, the call to pci_epc_set_bar() will fail,
+	 * and we will return failure back to the user.
+	 */
+	epf->bar[BAR_0].flags |= PCI_BASE_ADDRESS_MEM_TYPE_64;
 
 	/*
 	 * Calculate the size of the register bar: NVMe registers first with
-- 
2.48.1

Re: [PATCH v2] nvmet: pci-epf: Always configure BAR0 as 64-bit

[Chaitanya Kulkarni]

On 3/17/25 02:57, Niklas Cassel wrote:
> NVMe PCIe Transport Specification 1.1, section 2.1.10, claims that the
> BAR0 type is Implementation Specific.
>
> However, in NVMe 1.1, the type is required to be 64-bit.
>
> Thus, to make our PCI EPF work on as many host systems as possible,
> always configure the BAR0 type to be 64-bit.
>
> In the rare case that the underlying PCI EPC does not support configuring
> BAR0 as 64-bit, the call to pci_epc_set_bar() will fail, and we will
> return a failure back to the user.
>
> This should not be a problem, as most PCI EPCs support configuring a BAR
> as 64-bit (and those EPCs with .only_64bit set to true in epc_features
> only support configuring the BAR as 64-bit).
>
> Tested-by: Damien Le Moal<dlemoal@kernel.org>
> Fixes: 0faa0fe6f90e ("nvmet: New NVMe PCI endpoint function target driver")
> Signed-off-by: Niklas Cassel<cassel@kernel.org>

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck

Re: [PATCH v2] nvmet: pci-epf: Always configure BAR0 as 64-bit

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v2] nvmet: pci-epf: Always configure BAR0 as 64-bit

[Keith Busch]

On Mon, Mar 17, 2025 at 10:57:04AM +0100, Niklas Cassel wrote:
> NVMe PCIe Transport Specification 1.1, section 2.1.10, claims that the
> BAR0 type is Implementation Specific.
> 
> However, in NVMe 1.1, the type is required to be 64-bit.
> 
> Thus, to make our PCI EPF work on as many host systems as possible,
> always configure the BAR0 type to be 64-bit.
> 
> In the rare case that the underlying PCI EPC does not support configuring
> BAR0 as 64-bit, the call to pci_epc_set_bar() will fail, and we will
> return a failure back to the user.
> 
> This should not be a problem, as most PCI EPCs support configuring a BAR
> as 64-bit (and those EPCs with .only_64bit set to true in epc_features
> only support configuring the BAR as 64-bit).

Thanks, applied to nvme-6.15.