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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/4/24 05:07, Rick Edgecombe wrote: > Force TDX VMs to use the KVM_X86_QUIRK_SLOT_ZAP_ALL behavior. > > TDs cannot use the fast zapping operation to implement memslot deletion for > a couple reasons: > 1. KVM cannot fully zap and re-build TDX private PTEs without coordinating > with the guest. This is due to the TDs needing to "accept" memory. So > an operation to delete a memslot needs to limit the private zapping to > the range of the memslot. > 2. For reason (1), kvm_mmu_zap_all_fast() is limited to direct (shared) > roots. This means it will not zap the mirror (private) PTEs. If a > memslot is deleted with private memory mapped, the private memory would > remain mapped in the TD. Then if later the gmem fd was whole punched, > the pages could be freed on the host while still mapped in the TD. This > is because that operation would no longer have the memslot to map the > pgoff to the gfn. > > To handle the first case, userspace could simply set the > KVM_X86_QUIRK_SLOT_ZAP_ALL quirk for TDs. This would prevent the issue in > (1), but it is not sufficient to resolve (2) because the problems there > extend beyond the userspace's TD, to affecting the rest of the host. So the > zap-leafs-only behavior is required for both > > A couple options were considered, including forcing > KVM_X86_QUIRK_SLOT_ZAP_ALL to always be on for TDs, however due to the > currently limited quirks interface (no way to query quirks, or force them > to be disabled), this would require developing additional interfaces. So > instead just do the simple thing and make TDs always do the zap-leafs > behavior like when KVM_X86_QUIRK_SLOT_ZAP_ALL is disabled. > > While at it, have the new behavior apply to all non-KVM_X86_DEFAULT_VM VMs, > as the previous behavior was not ideal (see [0]). It is assumed until > proven otherwise that the other VM types will not be exposed to the bug[1] > that derailed that effort. > > Memslot deletion needs to zap both the private and shared mappings of a > GFN, so update the attr_filter field in kvm_mmu_zap_memslot_leafs() to > include both. > > Co-developed-by: Yan Zhao > Signed-off-by: Yan Zhao > Signed-off-by: Rick Edgecombe > Link: https://lore.kernel.org/kvm/20190205205443.1059-1-sean.j.christopherson@intel.com/ [0] > Link: https://patchwork.kernel.org/project/kvm/patch/20190205210137.1377-11-sean.j.christopherson@intel.com [1] > --- > TDX MMU part 2 v1: > - Clarify TDX limits on zapping private memory (Sean) > > Memslot quirk series: > - New patch > --- > arch/x86/kvm/mmu/mmu.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index a8d91cf11761..7e66d7c426c1 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -7104,6 +7104,7 @@ static void kvm_mmu_zap_memslot_leafs(struct kvm *kvm, struct kvm_memory_slot *s > .start = slot->base_gfn, > .end = slot->base_gfn + slot->npages, > .may_block = true, > + .attr_filter = KVM_FILTER_PRIVATE | KVM_FILTER_SHARED, > }; > bool flush = false; > Stale commit message, I guess. Paolo