Discussion:
[PATCH] x86,kvm,vmx: Don't trap writes to CR4.TSD
Andy Lutomirski
2014-10-08 00:16:21 UTC
Permalink
CR4.TSD is guest-owned; don't trap writes to it in VMX guests. This
avoids a VM exit on context switches into or out of a PR_TSC_SIGSEGV
task.

I think that this fixes an unintentional side-effect of:
4c38609ac569 KVM: VMX: Make guest cr4 mask more conservative

Signed-off-by: Andy Lutomirski <***@amacapital.net>
---
arch/x86/kvm/vmx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 54ca301f8415..0653233fcc82 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -105,7 +105,7 @@ module_param(nested, bool, S_IRUGO);
(KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST | X86_CR0_PG | X86_CR0_PE)
#define KVM_CR4_GUEST_OWNED_BITS \
(X86_CR4_PVI | X86_CR4_DE | X86_CR4_PCE | X86_CR4_OSFXSR \
- | X86_CR4_OSXMMEXCPT)
+ | X86_CR4_OSXMMEXCPT | X86_CR4_TSD)

#define KVM_PMODE_VM_CR4_ALWAYS_ON (X86_CR4_PAE | X86_CR4_VMXE)
#define KVM_RMODE_VM_CR4_ALWAYS_ON (X86_CR4_VME | X86_CR4_PAE | X86_CR4_VMXE)
--
1.9.3

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Andy Lutomirski
2014-10-22 19:10:20 UTC
Permalink
Post by Andy Lutomirski
CR4.TSD is guest-owned; don't trap writes to it in VMX guests. This
avoids a VM exit on context switches into or out of a PR_TSC_SIGSEGV
task.
Friendly ping. I suspect this got lost in KVM Forum, etc.

--Andy
Post by Andy Lutomirski
4c38609ac569 KVM: VMX: Make guest cr4 mask more conservative
---
arch/x86/kvm/vmx.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 54ca301f8415..0653233fcc82 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -105,7 +105,7 @@ module_param(nested, bool, S_IRUGO);
(KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST | X86_CR0_PG | X86_CR0_PE)
#define KVM_CR4_GUEST_OWNED_BITS \
(X86_CR4_PVI | X86_CR4_DE | X86_CR4_PCE | X86_CR4_OSFXSR \
- | X86_CR4_OSXMMEXCPT)
+ | X86_CR4_OSXMMEXCPT | X86_CR4_TSD)
#define KVM_PMODE_VM_CR4_ALWAYS_ON (X86_CR4_PAE | X86_CR4_VMXE)
#define KVM_RMODE_VM_CR4_ALWAYS_ON (X86_CR4_VME | X86_CR4_PAE | X86_CR4_VMXE)
--
1.9.3
--
Andy Lutomirski
AMA Capital Management, LLC
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Paolo Bonzini
2014-10-22 19:52:16 UTC
Permalink
Post by Andy Lutomirski
Post by Andy Lutomirski
CR4.TSD is guest-owned; don't trap writes to it in VMX guests. This
avoids a VM exit on context switches into or out of a PR_TSC_SIGSEGV
task.
Friendly ping. I suspect this got lost in KVM Forum, etc.
Yup, will push tomorrow.

Paolo
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