linux-kernel - Re: [PATCH] KVM: arm64: Fix 64 bit mmio handle

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Message-ID: <m2bkua148a.fsf@gmail.com>
Date:   Fri, 01 Jul 2022 00:50:59 +0800
From:   Schspa Shi <schspa@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: arm64: Fix 64 bit mmio handle


Marc Zyngier <maz@...nel.org> writes:

> On Thu, 30 Jun 2022 17:12:20 +0100,
> Schspa Shi <schspa@...il.com> wrote:
>> 
>> If the len is 8 bytes, we can't get the correct sign extend for
>> be system.
>
> I'm afraid you'll have to give me a bit more details.
>
>> 
>> Fix the mask type len and the comparison of length.
>> 
>> Signed-off-by: Schspa Shi <schspa@...il.com>
>> ---
>>  arch/arm64/kvm/mmio.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c
>> index 3dd38a151d2a6..0692f8b18f35c 100644
>> --- a/arch/arm64/kvm/mmio.c
>> +++ b/arch/arm64/kvm/mmio.c
>> @@ -81,8 +81,8 @@ unsigned long kvm_mmio_read_buf(const void 
>> *buf, unsigned int len)
>>  int kvm_handle_mmio_return(struct kvm_vcpu *vcpu)
>>  {
>>  	unsigned long data;
>> +	unsigned long mask;
>>  	unsigned int len;
>> -	int mask;
>>  
>>  	/* Detect an already handled MMIO return */
>>  	if (unlikely(!vcpu->mmio_needed))
>> @@ -97,7 +97,7 @@ int kvm_handle_mmio_return(struct kvm_vcpu 
>> *vcpu)
>>  		data = kvm_mmio_read_buf(run->mmio.data, len);
>>  
>>  		if (kvm_vcpu_dabt_issext(vcpu) &&
>> -		    len < sizeof(unsigned long)) {
>> +		    len <= sizeof(unsigned long)) {
>
> If you're reading an 8 byte quantity, what is there to 
> sign-extend?
> Sign extension only makes sense if what you're reading is 
> *smaller*
> than the size of the register you are targeting.
>

Yes, you are correct, sorry for my bad patch.
Please ignore this patch.

> I must be missing something. And how is that related to running 
> BE? BE
> in the host? The guest?

I mean BE is for guest running with BE mode.

>
> Please convince me.
>
> 	M.

-- 
BRs
Schspa Shi