linux-kernel - Re: [PATCH v12 13/46] KVM: x86: Prepare kvm_hv_flush

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Message-ID: <Y1m0HCMgwJen/NnU@google.com>
Date:   Wed, 26 Oct 2022 22:26:36 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 13/46] KVM: x86: Prepare kvm_hv_flush_tlb() to handle
 L2's GPAs

On Fri, Oct 21, 2022, Vitaly Kuznetsov wrote:
> To handle L2 TLB flush requests, KVM needs to translate the specified
> L2 GPA to L1 GPA to read hypercall arguments from there.
> 
> No functional change as KVM doesn't handle VMCALL/VMMCALL from L2 yet.
> 
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/hyperv.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index fca9c51891f5..df1efb821eb0 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -23,6 +23,7 @@
>  #include "ioapic.h"
>  #include "cpuid.h"
>  #include "hyperv.h"
> +#include "mmu.h"
>  #include "xen.h"
>  
>  #include <linux/cpu.h>
> @@ -1908,6 +1909,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  	 */
>  	BUILD_BUG_ON(KVM_HV_MAX_SPARSE_VCPU_SET_BITS > 64);
>  
> +	if (!hc->fast && is_guest_mode(vcpu)) {

Please add a comment explaining why only "slow" hypercalls need to translate the
GPA from L2=>L1.

With a comment (and assuming this isn't a bug),

Reviewed-by: Sean Christopherson <seanjc@...gle.com>