From: Naman Jain <[email protected]> Sent: Monday, April 6, 2026 2:25 AM > > When registering VTL0 memory via MSHV_ADD_VTL0_MEMORY, the kernel > computes pgmap->vmemmap_shift as the number of trailing zeros in the > OR of start_pfn and last_pfn, intending to use the largest compound > page order both endpoints are aligned to. > > However, this value is not clamped to MAX_FOLIO_ORDER, so a > sufficiently aligned range (e.g. physical range > [0x800000000000, 0x800080000000), corresponding to start_pfn=0x800000000 > with 35 trailing zeros) can produce a shift larger than what > memremap_pages() accepts, triggering a WARN and returning -EINVAL: > > WARNING: ... memremap_pages+0x512/0x650 > requested folio size unsupported > > The MAX_FOLIO_ORDER check was added by > commit 646b67d57589 ("mm/memremap: reject unreasonable folio/compound > page sizes in memremap_pages()"). > > Fix this by clamping vmemmap_shift to MAX_FOLIO_ORDER so we always > request the largest order the kernel supports, in those cases, rather > than an out-of-range value. > > Also fix the error path to propagate the actual error code from > devm_memremap_pages() instead of hard-coding -EFAULT, which was > masking the real -EINVAL return. > > Fixes: 7bfe3b8ea6e3 ("Drivers: hv: Introduce mshv_vtl driver") > Cc: [email protected] > Signed-off-by: Naman Jain <[email protected]> > --- > Changes since v1: > https://lore.kernel.org/all/20260401054005.1532381-1- > [email protected]/ > Addressed Michael's comments: > * remove MAX_FOLIO_ORDER value related text in commit msg > * Change change summary to keep prefix "mshv_vtl:" > * Add comments regarding last_pfn to avoid confusion > * use min instead of min_t > --- > drivers/hv/mshv_vtl_main.c | 12 +++++++++--- > include/uapi/linux/mshv.h | 2 +- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c > index 5856975f32e1..c19400701467 100644 > --- a/drivers/hv/mshv_vtl_main.c > +++ b/drivers/hv/mshv_vtl_main.c > @@ -386,7 +386,6 @@ static int mshv_vtl_ioctl_add_vtl0_mem(struct mshv_vtl > *vtl, void __user *arg) > > if (copy_from_user(&vtl0_mem, arg, sizeof(vtl0_mem))) > return -EFAULT; > - /* vtl0_mem.last_pfn is excluded in the pagemap range for VTL0 as per > design */ > if (vtl0_mem.last_pfn <= vtl0_mem.start_pfn) { > dev_err(vtl->module_dev, "range start pfn (%llx) > end pfn > (%llx)\n", > vtl0_mem.start_pfn, vtl0_mem.last_pfn); > @@ -397,6 +396,10 @@ static int mshv_vtl_ioctl_add_vtl0_mem(struct mshv_vtl > *vtl, void __user *arg) > if (!pgmap) > return -ENOMEM; > > + /* > + * vtl0_mem.last_pfn is excluded in the pagemap range for VTL0 as per > design. > + * last_pfn is not reserved or wasted, and reflects 'start_pfn + size' > of pagemap range. > + */ > pgmap->ranges[0].start = PFN_PHYS(vtl0_mem.start_pfn); > pgmap->ranges[0].end = PFN_PHYS(vtl0_mem.last_pfn) - 1; > pgmap->nr_range = 1; > @@ -405,8 +408,11 @@ static int mshv_vtl_ioctl_add_vtl0_mem(struct mshv_vtl > *vtl, void __user *arg) > /* > * Determine the highest page order that can be used for the given > memory range. > * This works best when the range is aligned; i.e. both the start and > the length. > + * Clamp to MAX_FOLIO_ORDER to avoid a WARN in memremap_pages() when > the range > + * alignment exceeds the maximum supported folio order for this kernel > config. > */ > - pgmap->vmemmap_shift = count_trailing_zeros(vtl0_mem.start_pfn | > vtl0_mem.last_pfn); > + pgmap->vmemmap_shift = min(count_trailing_zeros(vtl0_mem.start_pfn | > vtl0_mem.last_pfn), > + MAX_FOLIO_ORDER); > dev_dbg(vtl->module_dev, > "Add VTL0 memory: start: 0x%llx, end_pfn: 0x%llx, page order: > %lu\n", > vtl0_mem.start_pfn, vtl0_mem.last_pfn, pgmap->vmemmap_shift); > @@ -415,7 +421,7 @@ static int mshv_vtl_ioctl_add_vtl0_mem(struct mshv_vtl > *vtl, void __user *arg) > if (IS_ERR(addr)) { > dev_err(vtl->module_dev, "devm_memremap_pages error: %ld\n", > PTR_ERR(addr)); > kfree(pgmap); > - return -EFAULT; > + return PTR_ERR(addr); > } > > /* Don't free pgmap, since it has to stick around until the memory > diff --git a/include/uapi/linux/mshv.h b/include/uapi/linux/mshv.h > index e0645a34b55b..32ff92b6342b 100644 > --- a/include/uapi/linux/mshv.h > +++ b/include/uapi/linux/mshv.h > @@ -357,7 +357,7 @@ struct mshv_vtl_sint_post_msg { > > struct mshv_vtl_ram_disposition { > __u64 start_pfn; > - __u64 last_pfn; > + __u64 last_pfn; /* last_pfn is excluded from the range [start_pfn, > last_pfn) */ > }; > > struct mshv_vtl_set_poll_file { > -- > 2.43.0 >
Reviewed-by: Michael Kelley <[email protected]>
