Re: [PATCH kvmtool v2 13/22] hw/serial: Refactor trap handler

[Andre Przywara <andre.przywara@arm.com>]

On Fri, 12 Mar 2021 11:29:43 +0000
Alexandru Elisei <alexandru.elisei@arm.com> wrote:

> Hi Andre,
> 
> On 2/25/21 12:59 AM, 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.
> >
> > We drop the usage of ioport__read8/write8 entirely, as this would only
> > be applicable for I/O port accesses, and does nothing for 8-bit wide
> > accesses anyway.
> >
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > ---
> >  hw/serial.c | 93 +++++++++++++++++++++++++++++++++--------------------
> >  1 file changed, 58 insertions(+), 35 deletions(-)
> >
> > diff --git a/hw/serial.c b/hw/serial.c
> > index b0465d99..c495eac1 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;
> > @@ -317,7 +312,7 @@ static bool serial8250_out(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port
> >  	return ret;
> >  }
> >  
> > -static void serial8250_rx(struct serial8250_device *dev, void *data)
> > +static void serial8250_rx(struct serial8250_device *dev, u8 *data)
> >  {
> >  	if (dev->rxdone == dev->rxcnt)
> >  		return;
> > @@ -325,57 +320,54 @@ static void serial8250_rx(struct serial8250_device *dev, void *data)
> >  	/* Break issued ? */
> >  	if (dev->lsr & UART_LSR_BI) {
> >  		dev->lsr &= ~UART_LSR_BI;
> > -		ioport__write8(data, 0);
> > +		*data = 0;
> >  		return;
> >  	}
> >  
> > -	ioport__write8(data, dev->rxbuf[dev->rxdone++]);
> > +	*data = dev->rxbuf[dev->rxdone++];
> >  	if (dev->rxcnt == dev->rxdone) {
> >  		dev->lsr &= ~UART_LSR_DR;
> >  		dev->rxcnt = dev->rxdone = 0;
> >  	}
> >  }
> >  
> > -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 +381,37 @@ static bool serial8250_in(struct ioport *ioport, struct kvm_cpu *vcpu, u16 port,
> >  	return ret;
> >  }  
> 
> I'm not sure about replacing ioport_{read,write}8 with pointer dereferencing. They
> are functionally equivalent because big-endian and little-endian are about the
> order of bytes in memory, not the order of bits, but I don't think the change
> makes much sense because:
> 
> 1. All the other emulated devices use the ioport accessors, even in the case of 8
> bit accesses. For example, the RTC device uses ioport accessors and it too is
> converted in the end to a MMIO device, just like serial.
> 
> 2. The patch is about refactoring the emulation callbacks, other (non-trivial)
> changes should be a separate patch.
> 
> Please let me know if it's something that I'm missing. Other than this change, the
> patch looks good.

Well, I can see merits in both approaches: keeping the wrappers and
ditching them. Don't really have a strong opinion, but I think
eventually we should have the endian conversion in one central place
(in kvm__emulate_io()), where we can easily differentiate between port
I/O, MMIO and PCI accesses. Then all devices just need to dereference
pointers.
But this is indeed something for another time, and having wrappers
should not hurt either way, so I will keep them. Makes the patch smaller
anyway.

Cheers,
Andre

> >  
> > +static void serial8250_mmio(struct kvm_cpu *vcpu, u64 addr, u8 *data, u32 len,
> > +			    u8 is_write, void *ptr)
> > +{
> > +	struct serial8250_device *dev = ptr;
> > +
> > +	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;
> > +
> > +	serial8250_mmio(vcpu, port, data, 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;
> > +
> > +	serial8250_mmio(vcpu, port, data, 1, false, dev);
> > +
> > +	return true;
> > +}
> > +
> >  #ifdef CONFIG_HAS_LIBFDT
> >  
> >  char *fdt_stdout_path = NULL;
> > @@ -427,8 +450,8 @@ 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,