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

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Date:   Fri, 01 Jul 2022 11:50:01 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Schspa Shi <schspa@...il.com>
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

On 2022-06-30 17:50, Schspa Shi wrote:
> 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.

So what problem did you see? If you have noticed something going
wrong, I'd like to get it fixed.

Thanks,

          M.
-- 
Jazz is not dead. It just smells funny...