linux-kernel - Re: [PATCH 59/61] KVM: x86: Don't propagate MMU lpage support to memslot.disallow

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Date:   Tue, 25 Feb 2020 15:55:11 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 59/61] KVM: x86: Don't propagate MMU lpage support to memslot.disallow_lpage

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Stop propagating MMU large page support into a memslot's disallow_lpage
> now that the MMU's max_page_level handles the scenario where VMX's EPT is
> enabled and EPT doesn't support 2M pages.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 3 ---
>  arch/x86/kvm/x86.c     | 6 ++----
>  2 files changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 3ad24ca692a6..e349689ac0cf 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7633,9 +7633,6 @@ static __init int hardware_setup(void)
>  	if (!cpu_has_vmx_tpr_shadow())
>  		kvm_x86_ops->update_cr8_intercept = NULL;
>  
> -	if (enable_ept && !cpu_has_vmx_ept_2m_page())
> -		kvm_disable_largepages();
> -
>  #if IS_ENABLED(CONFIG_HYPERV)
>  	if (ms_hyperv.nested_features & HV_X64_NESTED_GUEST_MAPPING_FLUSH
>  	    && enable_ept) {
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 144143a57d0b..b40488fd2969 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9884,11 +9884,9 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
>  		ugfn = slot->userspace_addr >> PAGE_SHIFT;
>  		/*
>  		 * If the gfn and userspace address are not aligned wrt each
> -		 * other, or if explicitly asked to, disable large page
> -		 * support for this slot
> +		 * other, disable large page support for this slot.
>  		 */
> -		if ((slot->base_gfn ^ ugfn) & (KVM_PAGES_PER_HPAGE(level) - 1) ||
> -		    !kvm_largepages_enabled()) {
> +		if ((slot->base_gfn ^ ugfn) & (KVM_PAGES_PER_HPAGE(level) - 1)) {
>  			unsigned long j;
>  
>  			for (j = 0; j < lpages; ++j)

MMU code always explodes my brain, this left me wondering why wasn't the
original vmx_get_lpage_level() adjusted before...

FWIW,

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly