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From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Sean Christopherson <seanjc@google.com>
Cc: Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Babu Moger <babu.moger@amd.com>,
	Joao Martins <joao.m.martins@oracle.com>,
	David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [PATCH v2 7/9] KVM: x86/xen: Drop RAX[63:32] when processing hypercall
Date: Thu, 22 Apr 2021 12:35:06 +0200	[thread overview]
Message-ID: <2ddcc979-519c-a38c-065f-a9036cc2b58e@redhat.com> (raw)
In-Reply-To: <877dkuhcl7.fsf@vitty.brq.redhat.com>

On 22/04/21 11:51, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
>> Truncate RAX to 32 bits, i.e. consume EAX, when retrieving the hypecall
>> index for a Xen hypercall.  Per Xen documentation[*], the index is EAX
>> when the vCPU is not in 64-bit mode.
>>
>> [*] http://xenbits.xenproject.org/docs/sphinx-unstable/guest-guide/x86/hypercall-abi.html
>>
>> Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
>> Cc: Joao Martins <joao.m.martins@oracle.com>
>> Cc: David Woodhouse <dwmw@amazon.co.uk>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Sean Christopherson <seanjc@google.com>
>> ---
>>   arch/x86/kvm/xen.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
>> index ae17250e1efe..7f27bb65a572 100644
>> --- a/arch/x86/kvm/xen.c
>> +++ b/arch/x86/kvm/xen.c
>> @@ -673,7 +673,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
>>   	bool longmode;
>>   	u64 input, params[6];
>>   
>> -	input = (u64)kvm_register_read(vcpu, VCPU_REGS_RAX);
>> +	input = (u64)kvm_register_readl(vcpu, VCPU_REGS_RAX);
>>   
>>   	/* Hyper-V hypercalls get bit 31 set in EAX */
>>   	if ((input & 0x80000000) &&
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> Alternatively, as a minor optimization, you could've used '!longmode'
> check below, something like:
> 
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index ae17250e1efe..7df1498d3a41 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -682,6 +682,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
>   
>          longmode = is_64_bit_mode(vcpu);
>          if (!longmode) {
> +               input = (u32)input;
>                  params[0] = (u32)kvm_rbx_read(vcpu);
>                  params[1] = (u32)kvm_rcx_read(vcpu);
>                  params[2] = (u32)kvm_rdx_read(vcpu);
> 

You haven't seen patch 9 yet. :)

Paolo


  reply	other threads:[~2021-04-22 10:35 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-22  2:21 [PATCH v2 0/9] KVM: x86: Fixes for (benign?) truncation bugs Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 1/9] KVM: x86: Remove emulator's broken checks on CR0/CR3/CR4 loads Sean Christopherson
2021-04-22  6:50   ` Paolo Bonzini
2021-04-22  2:21 ` [PATCH v2 2/9] KVM: x86: Check CR3 GPA for validity regardless of vCPU mode Sean Christopherson
2021-04-22  6:51   ` Paolo Bonzini
2021-04-22 16:55     ` Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 3/9] KVM: SVM: Truncate GPR value for DR and CR accesses in !64-bit mode Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 4/9] KVM: VMX: Truncate GPR value for DR and CR reads " Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 5/9] KVM: nVMX: Truncate bits 63:32 of VMCS field on nested check in !64-bit Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 6/9] KVM: nVMX: Truncate base/index GPR value on address calc " Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 7/9] KVM: x86/xen: Drop RAX[63:32] when processing hypercall Sean Christopherson
2021-04-22  9:51   ` Vitaly Kuznetsov
2021-04-22 10:35     ` Paolo Bonzini [this message]
2021-04-22 10:49       ` Vitaly Kuznetsov
2021-04-22  2:21 ` [PATCH v2 8/9] KVM: SVM: Use default rAX size for INVLPGA emulation Sean Christopherson
2021-04-22  2:21 ` [PATCH v2 9/9] KVM: x86: Rename GPR accessors to make mode-aware variants the defaults Sean Christopherson
2021-04-22  6:55 ` [PATCH v2 0/9] KVM: x86: Fixes for (benign?) truncation bugs Paolo Bonzini

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