On Mon 07 Apr 2025 at 17:35, Niklas Cassel <cassel@xxxxxxxxxx> wrote:
> Hello Jerome,
>
> On Mon, Apr 07, 2025 at 04:39:08PM +0200, Jerome Brunet wrote:
>> When trying to allocate space for an endpoint function on a BAR with a
>> fixed size, the size saved in the 'struct pci_epf_bar' should be the fixed
>> size. This is expected by pci_epc_set_bar().
>>
>> However, if the fixed_size is smaller that the alignment, the size saved
>> in the 'struct pci_epf_bar' matches the alignment and it is a problem for
>> pci_epc_set_bar().
>>
>> To solve this, continue to allocate space that match the iATU alignment
>> requirement but save the size that matches what is present in the BAR.
>>
>> Fixes: 2a9a801620ef ("PCI: endpoint: Add support to specify alignment for buffers allocated to BARs")
>> Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>
>> ---
>> drivers/pci/endpoint/pci-epf-core.c | 25 +++++++++++++++++--------
>> 1 file changed, 17 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/endpoint/pci-epf-core.c b/drivers/pci/endpoint/pci-epf-core.c
>> index b7deb0ee1760b23a24f49abf3baf53ea2f273476..fb902b751e1c965c902c5199d57969ae0a757c2e 100644
>> --- a/drivers/pci/endpoint/pci-epf-core.c
>> +++ b/drivers/pci/endpoint/pci-epf-core.c
>> @@ -225,6 +225,7 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
>> struct device *dev;
>> struct pci_epf_bar *epf_bar;
>> struct pci_epc *epc;
>> + size_t size;
>>
>> if (!addr)
>> return;
>> @@ -237,9 +238,12 @@ void pci_epf_free_space(struct pci_epf *epf, void *addr, enum pci_barno bar,
>> epf_bar = epf->sec_epc_bar;
>> }
>>
>> + size = epf_bar[bar].size;
>> + if (epc_features->align)
>> + size = ALIGN(size, epc_features->align);
>
> Personally, I think that you should just save the aligned_size / mem_size /
> backing_mem_size as a new struct member, as that avoids the risk that someone
> later modifies pci_epf_alloc_space() but forgets to update
> pci_epf_free_space() accordingly.
I tried but it looked a bit silly to store that when it was only a
matter of calling ALIGN() with parameters we already had, and it is
supposed to be only used in those two functions.
>
> But I will leave the decision to the PCI endpoint maintainers.
>
Ultimately, I do not have a strong opinion on this. Either way is fine
by me.
>
> Kind regards,
> Niklas
>
>
>> +
>> dev = epc->dev.parent;
>> - dma_free_coherent(dev, epf_bar[bar].size, addr,
>> - epf_bar[bar].phys_addr);
>> + dma_free_coherent(dev, size, addr, epf_bar[bar].phys_addr);
>>
>> epf_bar[bar].phys_addr = 0;
>> epf_bar[bar].addr = NULL;
>> @@ -266,7 +270,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
>> enum pci_epc_interface_type type)
>> {
>> u64 bar_fixed_size = epc_features->bar[bar].fixed_size;
>> - size_t align = epc_features->align;
>> + size_t aligned_size, align = epc_features->align;
>> struct pci_epf_bar *epf_bar;
>> dma_addr_t phys_addr;
>> struct pci_epc *epc;
>> @@ -287,12 +291,17 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
>> return NULL;
>> }
>> size = bar_fixed_size;
>> + } else {
>> + /* BAR size must be power of two */
>> + size = roundup_pow_of_two(size);
>> }
>>
>> - if (align)
>> - size = ALIGN(size, align);
>> - else
>> - size = roundup_pow_of_two(size);
>> + /*
>> + * Allocate enough memory to accommodate the iATU alignment requirement.
>> + * In most cases, this will be the same as .size but it might be different
>> + * if, for example, the fixed size of a BAR is smaller than align
>> + */
>> + aligned_size = align ? ALIGN(size, align) : size;
>>
>> if (type == PRIMARY_INTERFACE) {
>> epc = epf->epc;
>> @@ -303,7 +312,7 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar,
>> }
>>
>> dev = epc->dev.parent;
>> - space = dma_alloc_coherent(dev, size, &phys_addr, GFP_KERNEL);
>> + space = dma_alloc_coherent(dev, aligned_size, &phys_addr, GFP_KERNEL);
>> if (!space) {
>> dev_err(dev, "failed to allocate mem space\n");
>> return NULL;
>>
>> --
>> 2.47.2
>>
--
Jerome
