| Message ID | 20240802181935.292540-1-seanjc@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: x86: Clean up MSR access/failure handling | expand |
On Fri, 02 Aug 2024 11:19:25 -0700, Sean Christopherson wrote: > Rework KVM's MSR access handling, and more specific the handling of failures, > to begin the march towards removing host_initiated exemptions for CPUID > checks, e.g. to eventually turn code like this: > > if (!msr_info->host_initiated && > !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES)) > return 1; > > [...] Applied to kvm-x86 misc, thanks! [01/10] KVM: SVM: Disallow guest from changing userspace's MSR_AMD64_DE_CFG value https://github.com/kvm-x86/linux/commit/74a0e79df68a [02/10] KVM: x86: Move MSR_TYPE_{R,W,RW} values from VMX to x86, as enums https://github.com/kvm-x86/linux/commit/b58b808cbe93 [03/10] KVM: x86: Rename KVM_MSR_RET_INVALID to KVM_MSR_RET_UNSUPPORTED https://github.com/kvm-x86/linux/commit/aaecae7b6a2b [04/10] KVM: x86: Refactor kvm_x86_ops.get_msr_feature() to avoid kvm_msr_entry https://github.com/kvm-x86/linux/commit/74c6c98a598a [05/10] KVM: x86: Rename get_msr_feature() APIs to get_feature_msr() https://github.com/kvm-x86/linux/commit/b848f24bd74a [06/10] KVM: x86: Refactor kvm_get_feature_msr() to avoid struct kvm_msr_entry https://github.com/kvm-x86/linux/commit/7075f1636150 [07/10] KVM: x86: Funnel all fancy MSR return value handling into a common helper https://github.com/kvm-x86/linux/commit/1cec2034980a [08/10] KVM: x86: Hoist x86.c's global msr_* variables up above kvm_do_msr_access() https://github.com/kvm-x86/linux/commit/3adef9034596 [09/10] KVM: x86: Suppress failures on userspace access to advertised, unsupported MSRs https://github.com/kvm-x86/linux/commit/64a5d7a1091f [10/10] KVM: x86: Suppress userspace access failures on unsupported, "emulated" MSRs https://github.com/kvm-x86/linux/commit/44dd0f5732b4 -- https://github.com/kvm-x86/linux/tree/next
Rework KVM's MSR access handling, and more specific the handling of failures, to begin the march towards removing host_initiated exemptions for CPUID checks, e.g. to eventually turn code like this: if (!msr_info->host_initiated && !guest_cpuid_has(vcpu, X86_FEATURE_XSAVES)) return 1; into if (!guest_cpuid_has(vcpu, X86_FEATURE_XSAVES)) return KVM_MSR_RET_UNSUPPORTED; For all intents and purposes, KVM already requires setting guest CPUID before setting MSRs, as there are multiple MSR flows that simply cannot work if CPUID isn't in place. But because KVM's ABI is that userspace is allowed to save/restore MSRs that are advertised to usersepace regardless of the vCPU CPUID model, KVM has ended up with code like the above where KVM unconditionally allows host accesses. The idea here is to funnel all MSR accesses through a single helper so that KVM can make the "host_initiated" exception in a single location based on KVM_MSR_RET_UNSUPPORTED, i.e. so that KVM doesn't need one-off checks for every MSR, which is especially problematic for CET where a Venn diagram is needed to map CET MSR existence to CPUID feature bits. This series doesn't actually remove the existing host_initiated checks. I *really* wanted to do that here, but removing all the existing checks is non-trivial and has a high chance of subtly breaking userspace. I still want to eventually get there, but it needs to be a slower, more thoughtful process. For now, the goal is to allow new features to omit the host_initiated checks without creating a weird userspace ABI, e.g to simplify the aforementioned CET support. v2: - Rebase (really the only reason I posted v2). - Collect reviews. [Weijiang] v1: - https://lore.kernel.org/all/20240425181422.3250947-1-seanjc@google.com Sean Christopherson (10): KVM: SVM: Disallow guest from changing userspace's MSR_AMD64_DE_CFG value KVM: x86: Move MSR_TYPE_{R,W,RW} values from VMX to x86, as enums KVM: x86: Rename KVM_MSR_RET_INVALID to KVM_MSR_RET_UNSUPPORTED KVM: x86: Refactor kvm_x86_ops.get_msr_feature() to avoid kvm_msr_entry KVM: x86: Rename get_msr_feature() APIs to get_feature_msr() KVM: x86: Refactor kvm_get_feature_msr() to avoid struct kvm_msr_entry KVM: x86: Funnel all fancy MSR return value handling into a common helper KVM: x86: Hoist x86.c's global msr_* variables up above kvm_do_msr_access() KVM: x86: Suppress failures on userspace access to advertised, unsupported MSRs KVM: x86: Suppress userspace access failures on unsupported, "emulated" MSRs arch/x86/include/asm/kvm-x86-ops.h | 2 +- arch/x86/include/asm/kvm_host.h | 2 +- arch/x86/kvm/svm/svm.c | 29 +- arch/x86/kvm/vmx/main.c | 2 +- arch/x86/kvm/vmx/vmx.c | 8 +- arch/x86/kvm/vmx/vmx.h | 4 - arch/x86/kvm/vmx/x86_ops.h | 2 +- arch/x86/kvm/x86.c | 513 ++++++++++++++--------------- arch/x86/kvm/x86.h | 21 +- 9 files changed, 294 insertions(+), 289 deletions(-) base-commit: 332d2c1d713e232e163386c35a3ba0c1b90df83f