Re: [RFC V1 PATCH 0/5] selftests: KVM: selftests for fd-based approach of supporting private memory

[Nikunj A. Dadhania]

On 4/9/2022 2:35 AM, Vishal Annapurve wrote:
> This series implements selftests targeting the feature floated by Chao
> via:
> https://lore.kernel.org/linux-mm/20220310140911.50924-1-chao.p.peng@xxxxxxxxxxxxxxx/
> 

Thanks for working on this.

> Below changes aim to test the fd based approach for guest private memory
> in context of normal (non-confidential) VMs executing on non-confidential
> platforms.
> 
> Confidential platforms along with the confidentiality aware software
> stack support a notion of private/shared accesses from the confidential
> VMs.
> Generally, a bit in the GPA conveys the shared/private-ness of the
> access. Non-confidential platforms don't have a notion of private or
> shared accesses from the guest VMs. To support this notion,
> KVM_HC_MAP_GPA_RANGE
> is modified to allow marking an access from a VM within a GPA range as
> always shared or private. Any suggestions regarding implementing this ioctl
> alternatively/cleanly are appreciated.
> 
> priv_memfd_test.c file adds a suite of two basic selftests to access private
> memory from the guest via private/shared access and checking if the contents
> can be leaked to/accessed by vmm via shared memory view.
> 
> Test results:
> 1) PMPAT - PrivateMemoryPrivateAccess test passes
> 2) PMSAT - PrivateMemorySharedAccess test fails currently and needs more
> analysis to understand the reason of failure.

That could be because of the return code (*r = -1) from the KVM_EXIT_MEMORY_ERROR. 
This gets interpreted as -EPERM in the VMM when the vcpu_run exits.

	+	vcpu->run->exit_reason = KVM_EXIT_MEMORY_ERROR;
	+	vcpu->run->memory.flags = flags;
	+	vcpu->run->memory.padding = 0;
	+	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
	+	vcpu->run->memory.size = PAGE_SIZE;
	+	fault->pfn = -1;
	+	*r = -1;
	+	return true;


Regards
Nikunj

[1] https://lore.kernel.org/all/20220310140911.50924-10-chao.p.peng@xxxxxxxxxxxxxxx/#t