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But, in this case, we are not going to get there >>> because we never send an r2 of size 0. >>> >>> For any non-zero size r2 the func will always return false because >>> the size 0 r1 cannot encompass any range. >>> >>> I could be misreading it all ;) >> >> The key is to know how a resource with size 0 is initialized, what can be >> understood looking at DEFINE_RES_NAMED macro. The end field is set as  size >> - 1. >> >> With unsigned variables, as it is the case here, it means to have a resource >> as big as possible ... if you do not check first the size is not 0. >> >> The pmem resource is explicitly initialized inside cxl_accel_state_create in >> the previous patch, so it has: >> >> pmem_res->start = 0, pmem_res.end = 0xffffffffffffffff >> >> the resource checked against is defined with, for example, a 256MB size: >> >> res.start =0, res.end = 0xfffffff >> >> >> if you then use resource_contains(pmem_res, res), that implies always true, >> whatever the res range defined. >> >> >> All this confused me as well when facing it initially. I hope this >> explanation makes sense. >> > Thanks for the explanation! I'm wondering if we are leaving a trap for the next > developer. > > resource_contains() seems to have intended that a check for IORESOURCE_UNSET > would take care of the zero size case: > > (5edb93b89f6c resource: Add resource_contains) > > and it would if folks used _UNSET. Some check r1->start before calling > resource_contains(). > > One option would be to use _UNSET in this case, but that only covers us here, > and doesn't remove the trap ;) > > How about hardening resource_contains(): > > ie: make resource_contains() return false if either res empty > > /* True iff r1 completely contains r2 */ > static inline bool resource_contains(const struct resource *r1, const struct resource *r2) > { > + if (!resource_size(r1) || !resource_size(r2)) > + return false; > if (resource_type(r1) != resource_type(r2)) > return false; > if (r1->flags & IORESOURCE_UNSET || r2->flags & IORESOURCE_UNSET) > return false; > return r1->start <= r2->start && r1->end >= r2->end; > } I can try that. If there is a good reason for not hardening it, we will know. Thanks! > -- Alison > >>> --Alison >>> >>> >>>> Add resource size check before using it. >>>> >>>> Signed-off-by: Alejandro Lucero >>>> --- >>>> drivers/cxl/core/hdm.c | 7 +++++-- >>>> 1 file changed, 5 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c >>>> index 223c273c0cd1..c58d6b8f9b58 100644 >>>> --- a/drivers/cxl/core/hdm.c >>>> +++ b/drivers/cxl/core/hdm.c >>>> @@ -327,10 +327,13 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled, >>>> cxled->dpa_res = res; >>>> cxled->skip = skipped; >>>> - if (resource_contains(&cxlds->pmem_res, res)) >>>> + if (resource_size(&cxlds->pmem_res) && >>>> + resource_contains(&cxlds->pmem_res, res)) { >>>> cxled->mode = CXL_DECODER_PMEM; >>>> - else if (resource_contains(&cxlds->ram_res, res)) >>>> + } else if (resource_size(&cxlds->ram_res) && >>>> + resource_contains(&cxlds->ram_res, res)) { >>>> cxled->mode = CXL_DECODER_RAM; >>>> + } >>>> else { >>>> dev_warn(dev, "decoder%d.%d: %pr mixed mode not supported\n", >>>> port->id, cxled->cxld.id, cxled->dpa_res); >>>> -- >>>> 2.17.1 >>>> >>>>