Sean Christopherson 66155de93b KVM: x86: Disallow read-only memslots for SEV-ES and SEV-SNP (and TDX) ... Disallow read-only memslots for SEV-{ES,SNP} VM types, as KVM can't directly emulate instructions for ES/SNP, and instead the guest must explicitly request emulation. Unless the guest explicitly requests emulation without accessing memory, ES/SNP relies on KVM creating an MMIO SPTE, with the subsequent #NPF being reflected into the guest as a #VC. But for read-only memslots, KVM deliberately doesn't create MMIO SPTEs, because except for ES/SNP, doing so requires setting reserved bits in the SPTE, i.e. the SPTE can't be readable while also generating a #VC on writes. Because KVM never creates MMIO SPTEs and jumps directly to emulation, the guest never gets a #VC. And since KVM simply resumes the guest if ES/SNP guests trigger emulation, KVM effectively puts the vCPU into an infinite #NPF loop if the vCPU attempts to write read-only memory. Disallow read-only memory for all VMs with protected state, i.e. for upcoming TDX VMs as well as ES/SNP VMs. For TDX, it's actually possible to support read-only memory, as TDX uses EPT Violation #VE to reflect the fault into the guest, e.g. KVM could configure read-only SPTEs with RX protections and SUPPRESS_VE=0. But there is no strong use case for supporting read-only memslots on TDX, e.g. the main historical usage is to emulate option ROMs, but TDX disallows executing from shared memory. And if someone comes along with a legitimate, strong use case, the restriction can always be lifted for TDX. Don't bother trying to retroactively apply the restriction to SEV-ES VMs that are created as type KVM_X86_DEFAULT_VM. Read-only memslots can't possibly work for SEV-ES, i.e. disallowing such memslots is really just means reporting an error to userspace instead of silently hanging vCPUs. Trying to deal with the ordering between KVM_SEV_INIT and memslot creation isn't worth the marginal benefit it would provide userspace. Fixes: 26c44aa9e0 ("KVM: SEV: define VM types for SEV and SEV-ES") Fixes: 1dfe571c12 ("KVM: SEV: Add initial SEV-SNP support") Cc: Peter Gonda <pgonda@google.com> Cc: Michael Roth <michael.roth@amd.com> Cc: Vishal Annapurve <vannapurve@google.com> Cc: Ackerly Tng <ackerleytng@google.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Message-ID: <20240809190319.1710470-2-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>		2024-08-14 12:28:24 -04:00
..
kvm	KVM: x86: Disallow read-only memslots for SEV-ES and SEV-SNP (and TDX)	2024-08-14 12:28:24 -04:00
lib	Revert "irqbypass: do not start cons/prod when failed connect"	2021-05-15 10:26:55 +01:00
Makefile	treewide: Add SPDX license identifier - Makefile/Kconfig	2019-05-21 10:50:46 +02:00