Re: [PATCH kvmtool 13/21] hw/serial: Refactor trap handler

Alexandru Elisei
2021-02-22T17:41:42Z

Hi Andre,

On 2/18/21 2:41 PM, Andre Przywara wrote:
> On Tue, 16 Feb 2021 14:22:05 +0000
> Alexandru Elisei <alexandru.elisei@arm.com> wrote:
>
>> Hi Andre,
>>
>> Patch looks good, nitpicks below.
>>
>> On 12/10/20 2:29 PM, Andre Przywara wrote:
>>> With the planned retirement of the special ioport emulation code, we
>>> need to provide an emulation function compatible with the MMIO prototype.
>>>
>>> Adjust the trap handler to use that new function, and provide shims to
>>> implement the old ioport interface, for now.
>>>
>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>> ---
>>> hw/serial.c | 97 +++++++++++++++++++++++++++++++++++------------------
>>> 1 file changed, 65 insertions(+), 32 deletions(-)
>>>
>>> diff --git a/hw/serial.c b/hw/serial.c
>>> index b0465d99..2907089c 100644
>>> --- a/hw/serial.c
>>> +++ b/hw/serial.c
>>> @@ -242,36 +242,31 @@ void serial8250__inject_sysrq(struct kvm *kvm, char sysrq)
>>> sysrq_pending = sysrq;
>>> }
>>>
>>> -static bool serial8250_out(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port,
>>> - void *data, int size)
>>> +static bool serial8250_out(struct serial8250_device *dev, struct kvm_cpu *vcpu,
>>> + u16 offset, u8 data)
>>> {
>>> - struct serial8250_device *dev = ioport->priv;
>>> - u16 offset;
>>> bool ret = true;
>>> - char *addr = data;
>>>
>>> mutex_lock(&dev->mutex);
>>>
>>> - offset = port - dev->iobase;
>>> -
>>> switch (offset) {
>>> case UART_TX:
>>> if (dev->lcr & UART_LCR_DLAB) {
>>> - dev->dll = ioport__read8(data);
>>> + dev->dll = data;
>>> break;
>>> }
>>>
>>> /* Loopback mode */
>>> if (dev->mcr & UART_MCR_LOOP) {
>>> if (dev->rxcnt < FIFO_LEN) {
>>> - dev->rxbuf[dev->rxcnt++] = *addr;
>>> + dev->rxbuf[dev->rxcnt++] = data;
>>> dev->lsr |= UART_LSR_DR;
>>> }
>>> break;
>>> }
>>>
>>> if (dev->txcnt < FIFO_LEN) {
>>> - dev->txbuf[dev->txcnt++] = *addr;
>>> + dev->txbuf[dev->txcnt++] = data;
>>> dev->lsr &= ~UART_LSR_TEMT;
>>> if (dev->txcnt == FIFO_LEN / 2)
>>> dev->lsr &= ~UART_LSR_THRE;
>>> @@ -283,18 +278,18 @@ static bool serial8250_out(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port
>>> break;
>>> case UART_IER:
>>> if (!(dev->lcr & UART_LCR_DLAB))
>>> - dev->ier = ioport__read8(data) & 0x0f;
>>> + dev->ier = data & 0x0f;
>>> else
>>> - dev->dlm = ioport__read8(data);
>>> + dev->dlm = data;
>>> break;
>>> case UART_FCR:
>>> - dev->fcr = ioport__read8(data);
>>> + dev->fcr = data;
>>> break;
>>> case UART_LCR:
>>> - dev->lcr = ioport__read8(data);
>>> + dev->lcr = data;
>>> break;
>>> case UART_MCR:
>>> - dev->mcr = ioport__read8(data);
>>> + dev->mcr = data;
>>> break;
>>> case UART_LSR:
>>> /* Factory test */
>>> @@ -303,7 +298,7 @@ static bool serial8250_out(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port
>>> /* Not used */
>>> break;
>>> case UART_SCR:
>>> - dev->scr = ioport__read8(data);
>>> + dev->scr = data;
>>> break;
>>> default:
>>> ret = false;
>>> @@ -336,46 +331,43 @@ static void serial8250_rx(struct serial8250_device *dev, void *data)
>>> }
>>> }
>>>
>>> -static bool serial8250_in(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port, void *data, int size)
>>> +static bool serial8250_in(struct serial8250_device *dev, struct kvm_cpu *vcpu,
>>> + u16 offset, u8 *data)
>>> {
>>> - struct serial8250_device *dev = ioport->priv;
>>> - u16 offset;
>>> bool ret = true;
>>>
>>> mutex_lock(&dev->mutex);
>>>
>>> - offset = port - dev->iobase;
>>> -
>>> switch (offset) {
>>> case UART_RX:
>>> if (dev->lcr & UART_LCR_DLAB)
>>> - ioport__write8(data, dev->dll);
>>> + *data = dev->dll;
>>> else
>>> serial8250_rx(dev, data);
>>> break;
>>> case UART_IER:
>>> if (dev->lcr & UART_LCR_DLAB)
>>> - ioport__write8(data, dev->dlm);
>>> + *data = dev->dlm;
>>> else
>>> - ioport__write8(data, dev->ier);
>>> + *data = dev->ier;
>>> break;
>>> case UART_IIR:
>>> - ioport__write8(data, dev->iir | UART_IIR_TYPE_BITS);
>>> + *data = dev->iir | UART_IIR_TYPE_BITS;
>>> break;
>>> case UART_LCR:
>>> - ioport__write8(data, dev->lcr);
>>> + *data = dev->lcr;
>>> break;
>>> case UART_MCR:
>>> - ioport__write8(data, dev->mcr);
>>> + *data = dev->mcr;
>>> break;
>>> case UART_LSR:
>>> - ioport__write8(data, dev->lsr);
>>> + *data = dev->lsr;
>>> break;
>>> case UART_MSR:
>>> - ioport__write8(data, dev->msr);
>>> + *data = dev->msr;
>>> break;
>>> case UART_SCR:
>>> - ioport__write8(data, dev->scr);
>>> + *data = dev->scr;
>>> break;
>>> default:
>>> ret = false;
>>> @@ -389,6 +381,47 @@ static bool serial8250_in(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port,
>>> return ret;
>>> }
>>>
>>> +static void serial8250_mmio(struct kvm_cpu *vcpu, u64 addr, u8 *data, u32 len,
>>> + u8 is_write, void *ptr)
>>> +{
>>> + struct serial8250_device *dev = ptr;
>>> + u8 value = 0;
>>> +
>>> + if (is_write) {
>>> + value = *data;
>> Extra space before value.
>>
>>> +
>>> + serial8250_out(dev, vcpu, addr - dev->iobase, value);
>>> + } else {
>>> + if (serial8250_in(dev, vcpu, addr - dev->iobase, &value))
>>> + *data = value;
>>> + }
>>> +}
>>> +
>>> +static bool serial8250_ioport_out(struct ioport *ioport, struct kvm_cpu *vcpu,
>>> + u16 port, void *data, int size)
>>> +{
>>> + struct serial8250_device *dev = ioport->priv;
>>> + u8 value = ioport__read8(data);
>>> +
>>> + serial8250_mmio(vcpu, port, &value, 1, true, dev);
>>> +
>>> + return true;
>>> +}
>>> +
>>> +static bool serial8250_ioport_in(struct ioport *ioport, struct kvm_cpu *vcpu,
>>> + u16 port, void *data, int size)
>>> +{
>>> + struct serial8250_device *dev = ioport->priv;
>>> + u8 value = 0;
>>> +
>>> +
>>> + serial8250_mmio(vcpu, port, &value, 1, false, dev);
>>> +
>>> + ioport__write8(data, value);
>> This is correct, but confusing. You pass the address of a local variable as *data
>> to serial8250_mmio, serial8250_mmio conditionally updates the value at data (which
>> is &value from here), and then here we update the *data unconditionally. Why not
>> pass data directly to serial8250_mmio and skip the local variable? Am I missing
>> something?
> The idea is to keep the abstraction of ioport__write<x>. I agree this
> is somewhat pointless for a single byte write, since the purpose of
> those wrappers is to deal with endianness, but it seems nice to use
> that anyway, anywhere, in case we need to add something to the wrappers
> at some point.

What I was thinking was something like this:

@@ -385,25 +386,19 @@ static void serial8250_mmio(struct kvm_cpu *vcpu, u64 addr,
u8 *data, u32 len,
u8 is_write, void *ptr)
{
struct serial8250_device *dev = ptr;
-       u8 value = 0;

-       if (is_write) {
-                value = *data;
-
-               serial8250_out(dev, vcpu, addr - dev->iobase, value);
-       } else {
-               if (serial8250_in(dev, vcpu, addr - dev->iobase, &value))
-                       *data = value;
-       }
+       if (is_write)
+               serial8250_out(dev, vcpu, addr - dev->iobase, data);
+       else
+               serial8250_in(dev, vcpu, addr - dev->iobase, data);
}

static bool serial8250_ioport_out(struct ioport *ioport, struct kvm_cpu *vcpu,
u16 port, void *data, int size)
{
struct serial8250_device *dev = ioport->priv;
-       u8 value = ioport__read8(data);

-       serial8250_mmio(vcpu, port, &value, 1, true, dev);
+       serial8250_mmio(vcpu, port, data, 1, true, dev);

return true;
}
@@ -412,12 +407,8 @@ static bool serial8250_ioport_in(struct ioport *ioport,
struct kvm_cpu *vcpu,
u16 port, void *data, int size)
{
struct serial8250_device *dev = ioport->priv;
-       u8 value = 0;
-
-
-       serial8250_mmio(vcpu, port, &value, 1, false, dev);

-       ioport__write8(data, value);
+       serial8250_mmio(vcpu, port, data, 1, false, dev);

return true;
}

And the ioport_{read,write}8 function will used inside the serial8250_{out,in}
functions, like they were before this patch, which should also make the diff
smaller. Or is there something that I'm missing which makes this unfeasible?

Thanks,

Alex

> ioport__write8() is a static inline in a header file, so it shouldn't
> really hurt, the compiler is able to see through it. The generated code
> is almost the same, at least.
>
> Let me know what you think!
>
> Cheers,
> Andre
>
>>> +
>>> + return true;
>>> +}
>>> +
>>> #ifdef CONFIG_HAS_LIBFDT
>>>
>>> char *fdt_stdout_path = NULL;
>>> @@ -427,8 +460,8 @@ void serial8250_generate_fdt_node(void *fdt, struct device_header *dev_hdr,
>>> #endif
>>>
>>> static struct ioport_operations serial8250_ops = {
>>> - .io_in = serial8250_in,
>>> - .io_out = serial8250_out,
>>> + .io_in = serial8250_ioport_in,
>>> + .io_out = serial8250_ioport_out,
>>> };
>>>
>>> static int serial8250__device_init(struct kvm *kvm,