On 03/09/20 16:11, Mohammed Gamal wrote:
> This patch exposes allow_smaller_maxphyaddr to the user as a module parameter.
>
> Since smaller physical address spaces are only supported on VMX, the parameter
> is only exposed in the kvm_intel module.
> Modifications to VMX page fault and EPT violation handling will depend on whether
> that parameter is enabled.
>
> Also disable support by default, and let the user decide if they want to enable
> it.
>
> Signed-off-by: Mohammed Gamal <mgamal@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/vmx.c | 15 ++++++---------
> arch/x86/kvm/vmx/vmx.h | 3 +++
> arch/x86/kvm/x86.c | 2 +-
> 3 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 819c185adf09..dc778c7b5a06 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -129,6 +129,9 @@ static bool __read_mostly enable_preemption_timer = 1;
> module_param_named(preemption_timer, enable_preemption_timer, bool, S_IRUGO);
> #endif
>
> +extern bool __read_mostly allow_smaller_maxphyaddr;
> +module_param(allow_smaller_maxphyaddr, bool, S_IRUGO | S_IWUSR);
> +
> #define KVM_VM_CR0_ALWAYS_OFF (X86_CR0_NW | X86_CR0_CD)
> #define KVM_VM_CR0_ALWAYS_ON_UNRESTRICTED_GUEST X86_CR0_NE
> #define KVM_VM_CR0_ALWAYS_ON \
> @@ -4798,7 +4801,8 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
>
> if (is_page_fault(intr_info)) {
> cr2 = vmx_get_exit_qual(vcpu);
> - if (enable_ept && !vcpu->arch.apf.host_apf_flags) {
> + if (enable_ept && !vcpu->arch.apf.host_apf_flags
> + && allow_smaller_maxphyaddr) {
> /*
> * EPT will cause page fault only if we need to
> * detect illegal GPAs.
> @@ -5331,7 +5335,7 @@ static int handle_ept_violation(struct kvm_vcpu *vcpu)
> * would also use advanced VM-exit information for EPT violations to
> * reconstruct the page fault error code.
> */
> - if (unlikely(kvm_mmu_is_illegal_gpa(vcpu, gpa)))
> + if (unlikely(kvm_mmu_is_illegal_gpa(vcpu, gpa)) && allow_smaller_maxphyaddr)
> return kvm_emulate_instruction(vcpu, 0);
>
> return kvm_mmu_page_fault(vcpu, gpa, error_code, NULL, 0);
> @@ -8303,13 +8307,6 @@ 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);
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 26175a4759fa..b859435efa2e 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -551,6 +551,9 @@ static inline bool vmx_has_waitpkg(struct vcpu_vmx *vmx)
>
> static inline bool vmx_need_pf_intercept(struct kvm_vcpu *vcpu)
> {
> + if (!allow_smaller_maxphyaddr)
> + return false;
> +
> return !enable_ept || cpuid_maxphyaddr(vcpu) < boot_cpu_data.x86_phys_bits;
This needs to return true if !enable_ept.
if (!enable_ept)
return true;
return allow_smaller_maxphyaddr &&
cpuid_maxphyaddr(vcpu) < boot_cpu_data.x86_phys_bits;
Fixed and queued, thanks.
Paolo
> }
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d39d6cf1d473..982f1d73a884 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -188,7 +188,7 @@ static struct kvm_shared_msrs __percpu *shared_msrs;
> u64 __read_mostly host_efer;
> EXPORT_SYMBOL_GPL(host_efer);
>
> -bool __read_mostly allow_smaller_maxphyaddr;
> +bool __read_mostly allow_smaller_maxphyaddr = 0;
> EXPORT_SYMBOL_GPL(allow_smaller_maxphyaddr);
>
> static u64 __read_mostly host_xss;
>
