Re: [PATCH v3 4/4] mshv: Handle insufficient root memory hypervisor statuses

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

On Thu, Feb 19, 2026 at 06:47:01AM +0000, Wei Liu wrote:
> On Fri, Feb 06, 2026 at 06:54:55PM +0000, Michael Kelley wrote:
> > From: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com> Sent: Thursday, February 5, 2026 10:42 AM
> > > To: kys@microsoft.com; haiyangz@microsoft.com; wei.liu@kernel.org;
> > > decui@microsoft.com; longli@microsoft.com
> > > Cc: linux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org
> > > Subject: [PATCH v3 4/4] mshv: Handle insufficient root memory hypervisor statuses
> > > 
> > > When creating guest partition objects, the hypervisor may fail to
> > > allocate root partition pages and return an insufficient memory status.
> > > In this case, deposit memory using the root partition ID instead.
> > > 
> > > Note: This error should never occur in a guest of L1VH partition context.
> > > 
> > > Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> > > ---
> > >  drivers/hv/hv_common.c      |    2 +
> > >  drivers/hv/hv_proc.c        |   14 ++++++++++
> > >  include/hyperv/hvgdk_mini.h |   58 ++++++++++++++++++++++---------------------
> > >  3 files changed, 46 insertions(+), 28 deletions(-)
> > > 
> > > diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> > > index f20596276662..6b67ac616789 100644
> > > --- a/drivers/hv/hv_common.c
> > > +++ b/drivers/hv/hv_common.c
> > > @@ -794,6 +794,8 @@ static const struct hv_status_info hv_status_infos[] = {
> > >  	_STATUS_INFO(HV_STATUS_PROPERTY_VALUE_OUT_OF_RANGE,	-EIO),
> > >  	_STATUS_INFO(HV_STATUS_INSUFFICIENT_MEMORY,		-ENOMEM),
> > >  	_STATUS_INFO(HV_STATUS_INSUFFICIENT_CONTIGUOUS_MEMORY,	-ENOMEM),
> > > +	_STATUS_INFO(HV_STATUS_INSUFFICIENT_ROOT_MEMORY,	-ENOMEM),
> > > +	_STATUS_INFO(HV_STATUS_INSUFFICIENT_CONTIGUOUS_ROOT_MEMORY, 	-ENOMEM),
> > >  	_STATUS_INFO(HV_STATUS_INVALID_PARTITION_ID,		-EINVAL),
> > >  	_STATUS_INFO(HV_STATUS_INVALID_VP_INDEX,		-EINVAL),
> > >  	_STATUS_INFO(HV_STATUS_NOT_FOUND,			-EIO),
> > > diff --git a/drivers/hv/hv_proc.c b/drivers/hv/hv_proc.c
> > > index 181f6d02bce3..5f4fd9c3231c 100644
> > > --- a/drivers/hv/hv_proc.c
> > > +++ b/drivers/hv/hv_proc.c
> > > @@ -121,6 +121,18 @@ int hv_deposit_memory_node(int node, u64 partition_id,
> > >  	case HV_STATUS_INSUFFICIENT_CONTIGUOUS_MEMORY:
> > >  		num_pages = HV_MAX_CONTIGUOUS_ALLOCATION_PAGES;
> > >  		break;
> > > +
> > > +	case HV_STATUS_INSUFFICIENT_CONTIGUOUS_ROOT_MEMORY:
> > > +		num_pages = HV_MAX_CONTIGUOUS_ALLOCATION_PAGES;
> > > +		fallthrough;
> > > +	case HV_STATUS_INSUFFICIENT_ROOT_MEMORY:
> > > +		if (!hv_root_partition()) {
> > > +			hv_status_err(hv_status, "Unexpected root memory deposit\n");
> > > +			return -ENOMEM;
> > > +		}
> > > +		partition_id = HV_PARTITION_ID_SELF;
> > > +		break;
> > > +
> > 
> > Per the discussion in v1 of this patch set, if the number of pages that should be
> > deposited in a particular situation is different from what this function provides,
> > the fallback is to use hv_call_deposit_pages() directly. From what I see, there's
> > only one such fallback case after a hypercall failure -- in hv_do_map_gpa_hcall().
> > The other uses of hv_call_deposit_pages() are initial deposits when creating a
> > VP or partition.
> > 
> > But if hv_call_deposit_pages() is used directly, the logic added here to detect
> > insufficient root memory and deposit to HV_PARTITION_ID_SELF isn't applied.
> > So if the hypercall in hv_do_map_gpa_hcall() fails with insufficient root
> > memory, the deposit is done to the wrong partition ID. If that case can
> > actually happen, then some additional logic is needed in
> > hv_do_map_gpa_hcall() to handle it. Or there needs to be a fallback
> > function that contains the logic.
> 
> Stanislav, how about this comment? Please submit a follow-up patch if
> necessary.
> 

I'll sumbit a follow-up patch.

Thanks,
Stanislav

> Wei
> 
> > 
> > Other than that, everything else in this patch set looks good to me.
> > 
> > Michael
> > 
> > >  	default:
> > >  		hv_status_err(hv_status, "Unexpected!\n");
> > >  		return -ENOMEM;