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KVM: x86: Allow deflecting unknown MSR accesses to user space

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MSRs are weird. Some of them are normal control registers, such as EFER.
Some however are registers that really are model specific, not very
interesting to virtualization workloads, and not performance critical.
Others again are really just windows into package configuration.

Out of these MSRs, only the first category is necessary to implement in
kernel space. Rarely accessed MSRs, MSRs that should be fine tunes against
certain CPU models and MSRs that contain information on the package level
are much better suited for user space to process. However, over time we have
accumulated a lot of MSRs that are not the first category, but still handled
by in-kernel KVM code.

This patch adds a generic interface to handle WRMSR and RDMSR from user
space. With this, any future MSR that is part of the latter categories can
be handled in user space.

Furthermore, it allows us to replace the existing "ignore_msrs" logic with
something that applies per-VM rather than on the full system. That way you
can run productive VMs in parallel to experimental ones where you don't care
about proper MSR handling.

Signed-off-by: Alexander Graf <graf@amazon.com>
Reviewed-by: Jim Mattson <jmattson@google.com>

Message-Id: <20200925143422.21718-3-graf@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alexander Graf
2020-09-25 16:34:16 +02:00
committed by Paolo Bonzini
parent 90218e434c
commit 1ae099540e
6 changed files with 226 additions and 15 deletions
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13
include/uapi/linux/kvm.h
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@@ -248,6 +248,8 @@ struct kvm_hyperv_exit {
#define KVM_EXIT_IOAPIC_EOI 26
#define KVM_EXIT_HYPERV 27
#define KVM_EXIT_ARM_NISV 28
#define KVM_EXIT_X86_RDMSR 29
#define KVM_EXIT_X86_WRMSR 30
/* For KVM_EXIT_INTERNAL_ERROR */
/* Emulate instruction failed. */
@@ -413,6 +415,16 @@ struct kvm_run {
__u64 esr_iss;
__u64 fault_ipa;
} arm_nisv;
/* KVM_EXIT_X86_RDMSR / KVM_EXIT_X86_WRMSR */
struct {
__u8 error; /* user -> kernel */
__u8 pad[7];
#define KVM_MSR_EXIT_REASON_INVAL (1 << 0)
#define KVM_MSR_EXIT_REASON_UNKNOWN (1 << 1)
__u32 reason; /* kernel -> user */
__u32 index; /* kernel -> user */
__u64 data; /* kernel <-> user */
} msr;
/* Fix the size of the union. */
char padding[256];
};
@@ -1037,6 +1049,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_SMALLER_MAXPHYADDR 185
#define KVM_CAP_S390_DIAG318 186
#define KVM_CAP_STEAL_TIME 187
#define KVM_CAP_X86_USER_SPACE_MSR 188
#ifdef KVM_CAP_IRQ_ROUTING