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SubjectRe: [PATCH 2/2] arm:kvm remove len 8 for mmio read write buf
Just began learning this piece of code.
Thanks for correcting me.

On 12/22/2014 07:51 PM, Marc Zyngier wrote:
> On 22/12/14 11:23, Peng Fan wrote:
>> For arm 32 bit architecture, 8 bytes load/store operation in one instruction
>> will not be generated by compiler.
>
> Ever heard of lrdr/strd?
>
>> And before invoke mmio_read_buf, there is a piece of code:
>> "
>> len = run->mmio.len;
>> if (len > sizeof(unsigned long))
>> return -EINVAL;
>>
>> data = mmio_read_buf(run->mmio.data, len);
>> "
>>
>> This piece code also tells that len variable does not exceeds 4 bytes.
>> So, remove 8 bytes assign in mmio_read_buf and mmio_write_buf.
>
> NAK. This code is shared between arm and arm64. See commit f42798c.
>
> M.
>
>>
>> Signed-off-by: Peng Fan <van.freenix@gmail.com>
>> CC: Gleb Natapov <gleb@kernel.org>
>> CC: Paolo Bonzini <pbonzini@redhat.com>
>> CC: Christoffer Dall <christoffer.dall@linaro.org>
>> CC: Marc Zyngier <marc.zyngier@arm.com>
>> CC: Russell King <linux@arm.linux.org.uk>
>> ---
>> arch/arm/kvm/mmio.c | 10 ----------
>> 1 file changed, 10 deletions(-)
>>
>> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
>> index 4cb5a93..953a819 100644
>> --- a/arch/arm/kvm/mmio.c
>> +++ b/arch/arm/kvm/mmio.c
>> @@ -30,7 +30,6 @@ static void mmio_write_buf(char *buf, unsigned int len, unsigned long data)
>> u8 byte;
>> u16 hword;
>> u32 word;
>> - u64 dword;
>> } tmp;
>>
>> switch (len) {
>> @@ -46,10 +45,6 @@ static void mmio_write_buf(char *buf, unsigned int len, unsigned long data)
>> tmp.word = data;
>> datap = &tmp.word;
>> break;
>> - case 8:
>> - tmp.dword = data;
>> - datap = &tmp.dword;
>> - break;
>> }
>>
>> memcpy(buf, datap, len);
>> @@ -61,7 +56,6 @@ static unsigned long mmio_read_buf(char *buf, unsigned int len)
>> union {
>> u16 hword;
>> u32 word;
>> - u64 dword;
>> } tmp;
>>
>> switch (len) {
>> @@ -76,10 +70,6 @@ static unsigned long mmio_read_buf(char *buf, unsigned int len)
>> memcpy(&tmp.word, buf, len);
>> data = tmp.word;
>> break;
>> - case 8:
>> - memcpy(&tmp.dword, buf, len);
>> - data = tmp.dword;
>> - break;
>> }
>>
>> return data;
>>
>
>


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