linux/Documentation/virt, branch v6.8

Merge tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm

2024-03-10T16:27:39Z

Pull kvm fixes from Paolo Bonzini: "KVM GUEST_MEMFD fixes for 6.8: - Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY to avoid creating an inconsistent ABI (KVM_MEM_GUEST_MEMFD is not writable from userspace, so there would be no way to write to a read-only guest_memfd). - Update documentation for KVM_SW_PROTECTED_VM to make it abundantly clear that such VMs are purely for development and testing. - Limit KVM_SW_PROTECTED_VM guests to the TDP MMU, as the long term plan is to support confidential VMs with deterministic private memory (SNP and TDX) only in the TDP MMU. - Fix a bug in a GUEST_MEMFD dirty logging test that caused false passes. x86 fixes: - Fix missing marking of a guest page as dirty when emulating an atomic access. - Check for mmu_notifier invalidation events before faulting in the pfn, and before acquiring mmu_lock, to avoid unnecessary work and lock contention with preemptible kernels (including CONFIG_PREEMPT_DYNAMIC in non-preemptible mode). - Disable AMD DebugSwap by default, it breaks VMSA signing and will be re-enabled with a better VM creation API in 6.10. - Do the cache flush of converted pages in svm_register_enc_region() before dropping kvm->lock, to avoid a race with unregistering of the same region and the consequent use-after-free issue" * tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: SEV: disable SEV-ES DebugSwap by default KVM: x86/mmu: Retry fault before acquiring mmu_lock if mapping is changing KVM: SVM: Flush pages under kvm->lock to fix UAF in svm_register_enc_region() KVM: selftests: Add a testcase to verify GUEST_MEMFD and READONLY are exclusive KVM: selftests: Create GUEST_MEMFD for relevant invalid flags testcases KVM: x86/mmu: Restrict KVM_SW_PROTECTED_VM to the TDP MMU KVM: x86: Update KVM_SW_PROTECTED_VM docs to make it clear they're a WIP KVM: Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY KVM: x86: Mark target gfn of emulated atomic instruction as dirty

Documentation: hyperv: Add overview of PCI pass-thru device support

2024-03-01T08:29:49Z

Add documentation topic for PCI pass-thru devices in Linux guests on Hyper-V and for the associated PCI controller driver (pci-hyperv.c). Signed-off-by: Michael Kelley Reviewed-by: Easwar Hariharan Link: https://lore.kernel.org/r/20240222200710.305259-1-mhklinux@outlook.com Signed-off-by: Wei Liu Message-ID: <20240222200710.305259-1-mhklinux@outlook.com>

KVM: x86: Update KVM_SW_PROTECTED_VM docs to make it clear they're a WIP

2024-02-23T01:07:06Z

Rewrite the help message for KVM_SW_PROTECTED_VM to make it clear that software-protected VMs are a development and testing vehicle for guest_memfd(), and that attempting to use KVM_SW_PROTECTED_VM for anything remotely resembling a "real" VM will fail. E.g. any memory accesses from KVM will incorrectly access shared memory, nested TDP is wildly broken, and so on and so forth. Update KVM's API documentation with similar warnings to discourage anyone from attempting to run anything but selftests with KVM_X86_SW_PROTECTED_VM. Fixes: 89ea60c2c7b5 ("KVM: x86: Add support for "protected VMs" that can utilize private memory") Link: https://lore.kernel.org/r/20240222190612.2942589-3-seanjc@google.com Signed-off-by: Sean Christopherson

Merge tag 'kvm-x86-mmu-6.8' of https://github.com/kvm-x86/linux into HEAD

2024-01-08T13:10:32Z

KVM x86 MMU changes for 6.8: - Fix a relatively benign off-by-one error when splitting huge pages during CLEAR_DIRTY_LOG. - Fix a bug where KVM could incorrectly test-and-clear dirty bits in non-leaf TDP MMU SPTEs if a racing thread replaces a huge SPTE with a non-huge SPTE. - Relax the TDP MMU's lockdep assertions related to holding mmu_lock for read versus write so that KVM doesn't pass "bool shared" all over the place just to have precise assertions in paths that don't actually care about whether the caller is a reader or a writer.

Merge tag 'kvm-x86-xen-6.8' of https://github.com/kvm-x86/linux into HEAD

2024-01-08T13:10:20Z

KVM Xen change for 6.8: To workaround Xen guests that don't expect Xen PV clocks to be marked as being based on a stable TSC, add a Xen config knob to allow userspace to opt out of KVM setting the "TSC stable" bit in Xen PV clocks. Note, the "TSC stable" bit was added to the PVCLOCK ABI by KVM without an ack from Xen, i.e. KVM isn't entirely blameless for the buggy guest behavior.

KVM: remove deprecated UAPIs

2023-12-08T20:43:33Z

The deprecated interfaces were removed 15 years ago. KVM's device assignment was deprecated in 4.2 and removed 6.5 years ago; the only interest might be in compiling ancient versions of QEMU, but QEMU has been using its own imported copy of the kernel headers since June 2011. So again we go into archaeology territory; just remove the cruft. Signed-off-by: Paolo Bonzini

KVM x86/xen: add an override for PVCLOCK_TSC_STABLE_BIT

2023-12-07T23:52:57Z

Unless explicitly told to do so (by passing 'clocksource=tsc' and 'tsc=stable:socket', and then jumping through some hoops concerning potential CPU hotplug) Xen will never use TSC as its clocksource. Hence, by default, a Xen guest will not see PVCLOCK_TSC_STABLE_BIT set in either the primary or secondary pvclock memory areas. This has led to bugs in some guest kernels which only become evident if PVCLOCK_TSC_STABLE_BIT *is* set in the pvclocks. Hence, to support such guests, give the VMM a new Xen HVM config flag to tell KVM to forcibly clear the bit in the Xen pvclocks. Signed-off-by: Paul Durrant Reviewed-by: David Woodhouse Link: https://lore.kernel.org/r/20231102162128.2353459-1-paul@xen.org Signed-off-by: Sean Christopherson

KVM: x86/mmu: always take tdp_mmu_pages_lock

2023-12-01T15:52:08Z

It is cheap to take tdp_mmu_pages_lock in all write-side critical sections. We already do it all the time when zapping with read_lock(), so it is not a problem to do it from the kvm_tdp_mmu_zap_all() path (aka kvm_arch_flush_shadow_all(), aka VM destruction and MMU notifier release). Signed-off-by: Paolo Bonzini Link: https://lore.kernel.org/r/20231125083400.1399197-4-pbonzini@redhat.com Signed-off-by: Sean Christopherson

KVM: x86: Add support for "protected VMs" that can utilize private memory

2023-11-14T13:01:05Z

Add a new x86 VM type, KVM_X86_SW_PROTECTED_VM, to serve as a development and testing vehicle for Confidential (CoCo) VMs, and potentially to even become a "real" product in the distant future, e.g. a la pKVM. The private memory support in KVM x86 is aimed at AMD's SEV-SNP and Intel's TDX, but those technologies are extremely complex (understatement), difficult to debug, don't support running as nested guests, and require hardware that's isn't universally accessible. I.e. relying SEV-SNP or TDX for maintaining guest private memory isn't a realistic option. At the very least, KVM_X86_SW_PROTECTED_VM will enable a variety of selftests for guest_memfd and private memory support without requiring unique hardware. Signed-off-by: Sean Christopherson Reviewed-by: Paolo Bonzini Message-Id: <20231027182217.3615211-24-seanjc@google.com> Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Signed-off-by: Paolo Bonzini

KVM: x86/mmu: Handle page fault for private memory

2023-11-14T13:01:04Z

Add support for resolving page faults on guest private memory for VMs that differentiate between "shared" and "private" memory. For such VMs, KVM_MEM_GUEST_MEMFD memslots can include both fd-based private memory and hva-based shared memory, and KVM needs to map in the "correct" variant, i.e. KVM needs to map the gfn shared/private as appropriate based on the current state of the gfn's KVM_MEMORY_ATTRIBUTE_PRIVATE flag. For AMD's SEV-SNP and Intel's TDX, the guest effectively gets to request shared vs. private via a bit in the guest page tables, i.e. what the guest wants may conflict with the current memory attributes. To support such "implicit" conversion requests, exit to user with KVM_EXIT_MEMORY_FAULT to forward the request to userspace. Add a new flag for memory faults, KVM_MEMORY_EXIT_FLAG_PRIVATE, to communicate whether the guest wants to map memory as shared vs. private. Like KVM_MEMORY_ATTRIBUTE_PRIVATE, use bit 3 for flagging private memory so that KVM can use bits 0-2 for capturing RWX behavior if/when userspace needs such information, e.g. a likely user of KVM_EXIT_MEMORY_FAULT is to exit on missing mappings when handling guest page fault VM-Exits. In that case, userspace will want to know RWX information in order to correctly/precisely resolve the fault. Note, private memory *must* be backed by guest_memfd, i.e. shared mappings always come from the host userspace page tables, and private mappings always come from a guest_memfd instance. Co-developed-by: Yu Zhang Signed-off-by: Yu Zhang Signed-off-by: Chao Peng Co-developed-by: Sean Christopherson Signed-off-by: Sean Christopherson Reviewed-by: Fuad Tabba Tested-by: Fuad Tabba Message-Id: <20231027182217.3615211-21-seanjc@google.com> Signed-off-by: Paolo Bonzini