diff options
| author | Mohammed Gamal <mgamal@redhat.com> | 2020-07-10 17:48:11 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2020-07-10 17:01:53 -0400 |
| commit | 3edd68399dc155b80335244c8c2673eaa652931a (patch) | |
| tree | c9416694c43d066b4fa198d8c42e5ec3e729a04c /arch/x86/kvm/vmx | |
| parent | 8c4182bd27cafc2b0f94564485c89ed366c1572c (diff) | |
KVM: x86: Add a capability for GUEST_MAXPHYADDR < HOST_MAXPHYADDR support
This patch adds a new capability KVM_CAP_SMALLER_MAXPHYADDR which
allows userspace to query if the underlying architecture would
support GUEST_MAXPHYADDR < HOST_MAXPHYADDR and hence act accordingly
(e.g. qemu can decide if it should warn for -cpu ..,phys-bits=X)
The complications in this patch are due to unexpected (but documented)
behaviour we see with NPF vmexit handling in AMD processor. If
SVM is modified to add guest physical address checks in the NPF
and guest #PF paths, we see the followning error multiple times in
the 'access' test in kvm-unit-tests:
test pte.p pte.36 pde.p: FAIL: pte 2000021 expected 2000001
Dump mapping: address: 0x123400000000
------L4: 24c3027
------L3: 24c4027
------L2: 24c5021
------L1: 1002000021
This is because the PTE's accessed bit is set by the CPU hardware before
the NPF vmexit. This is handled completely by hardware and cannot be fixed
in software.
Therefore, availability of the new capability depends on a boolean variable
allow_smaller_maxphyaddr which is set individually by VMX and SVM init
routines. On VMX it's always set to true, on SVM it's only set to true
when NPT is not enabled.
CC: Tom Lendacky <thomas.lendacky@amd.com>
CC: Babu Moger <babu.moger@amd.com>
Signed-off-by: Mohammed Gamal <mgamal@redhat.com>
Message-Id: <20200710154811.418214-10-mgamal@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/vmx')
| -rw-r--r-- | arch/x86/kvm/vmx/vmx.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 962a78c7dde5..1bb59ae5016d 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -8309,6 +8309,13 @@ static int __init vmx_init(void) #endif vmx_check_vmcs12_offsets(); + /* + * Intel processors don't have problems with + * GUEST_MAXPHYADDR < HOST_MAXPHYADDR so enable + * it for VMX by default + */ + allow_smaller_maxphyaddr = true; + return 0; } module_init(vmx_init); |