This is a largely untested series to do most of what was discussed in the thread regarding locking issues between gmem and TDX's post-populate hook[*], with more than a few side quests thrown in as I was navigating through the code to try to figure out how best to eliminate the copy_from_user() from sev_gmem_post_populate(), which has the same locking problem (copying from a userspace address can fault and in theory trigger the same problematic path, I think). Notably absent is the extraction of copy_from_user() from sev_gmem_post_populate() to kvm_gmem_populate(). I've had this on my todo list for a few weeks now, and haven't been able to focus on it for long enough to get something hammered out, and with KVM Forum on the horizon, I don't anticipate getting 'round to it within the next month (if not much longer). The thing that stymied me is what to do if snp_launch_update() is passed in a huge batch of pages. I waffled between doing a slow one-at-a-time approach and a batched approached, and got especially stuck when trying to remember and/or figure out how that handling would interact with hugepage support in SNP in particular. If anyone wants to tackle that project, the one thing change I definitely think we should do is change the post_populate() callback to operate on exactly one page. KVM_SEV_SNP_LAUNCH_UPDATE allows for partial progress, i.e. KVM's ABI doesn't require it to unwind a batch if adding a page fails. If we take advantage of that, then sev_gmem_post_populate() will be a bit simpler (though I wouldn't go so far as to call it "simple"). RFC as this is compile tested only (mostly due to lack of access to a TDX capable system, but also due to lack of cycles). [*] http://lore.kernel.org/all/aG_pLUlHdYIZ2luh@xxxxxxxxxx Sean Christopherson (12): KVM: TDX: Drop PROVE_MMU=y sanity check on to-be-populated mappings KVM: x86/mmu: Add dedicated API to map guest_memfd pfn into TDP MMU Revert "KVM: x86/tdp_mmu: Add a helper function to walk down the TDP MMU" KVM: x86/mmu: Rename kvm_tdp_map_page() to kvm_tdp_prefault_page() KVM: TDX: Drop superfluous page pinning in S-EPT management KVM: TDX: Return -EIO, not -EINVAL, on a KVM_BUG_ON() condition KVM: TDX: Avoid a double-KVM_BUG_ON() in tdx_sept_zap_private_spte() KVM: TDX: Use atomic64_dec_return() instead of a poor equivalent KVM: TDX: Fold tdx_mem_page_record_premap_cnt() into its sole caller KVM: TDX: Assert that slots_lock is held when nr_premapped is accessed KVM: TDX: Track nr_premapped as an "unsigned long", not an "atomic64_t" KVM: TDX: Rename nr_premapped to nr_pending_tdh_mem_page_adds arch/x86/kvm/mmu.h | 3 +- arch/x86/kvm/mmu/mmu.c | 66 ++++++++++++++++++-- arch/x86/kvm/mmu/tdp_mmu.c | 37 ++--------- arch/x86/kvm/vmx/tdx.c | 123 +++++++++++++------------------------ arch/x86/kvm/vmx/tdx.h | 9 ++- 5 files changed, 117 insertions(+), 121 deletions(-) base-commit: 196d9e72c4b0bd68b74a4ec7f52d248f37d0f030 -- 2.51.0.268.g9569e192d0-goog
