Re: [PATCH v2 kvmtool 26/30] pci: Toggle BAR I/O and memory space emulation

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

On Thu, 23 Jan 2020 13:48:01 +0000
Alexandru Elisei <alexandru.elisei@arm.com> wrote:

Hi,

> During configuration of the BAR addresses, a Linux guest disables and
> enables access to I/O and memory space. When access is disabled, we don't
> stop emulating the memory regions described by the BARs. Now that we have
> callbacks for activating and deactivating emulation for a BAR region,
> let's use that to stop emulation when access is disabled, and
> re-activate it when access is re-enabled.
> 
> The vesa emulation hasn't been designed with toggling on and off in
> mind, so refuse writes to the PCI command register that disable memory
> or IO access.
> 
> Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> ---
>  hw/vesa.c | 16 ++++++++++++++++
>  pci.c     | 42 ++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/hw/vesa.c b/hw/vesa.c
> index 74ebebbefa6b..3044a86078fb 100644
> --- a/hw/vesa.c
> +++ b/hw/vesa.c
> @@ -81,6 +81,18 @@ static int vesa__bar_deactivate(struct kvm *kvm,
>  	return -EINVAL;
>  }
>  
> +static void vesa__pci_cfg_write(struct kvm *kvm, struct pci_device_header *pci_hdr,
> +				u8 offset, void *data, int sz)
> +{
> +	u32 value;

I guess the same comment as on the other patch applies: using u64 looks safer to me. Also you should clear it, to avoid nasty surprises in case of a short write (1 or 2 bytes only).

The rest looks alright.

Cheers,
Andre

> +
> +	if (offset == PCI_COMMAND) {
> +		memcpy(&value, data, sz);
> +		value |= (PCI_COMMAND_IO | PCI_COMMAND_MEMORY);
> +		memcpy(data, &value, sz);
> +	}
> +}
> +
>  struct framebuffer *vesa__init(struct kvm *kvm)
>  {
>  	struct vesa_dev *vdev;
> @@ -114,6 +126,10 @@ struct framebuffer *vesa__init(struct kvm *kvm)
>  		.bar_size[1]		= VESA_MEM_SIZE,
>  	};
>  
> +	vdev->pci_hdr.cfg_ops = (struct pci_config_operations) {
> +		.write	= vesa__pci_cfg_write,
> +	};
> +
>  	vdev->fb = (struct framebuffer) {
>  		.width			= VESA_WIDTH,
>  		.height			= VESA_HEIGHT,
> diff --git a/pci.c b/pci.c
> index 5412f2defa2e..98331a1fc205 100644
> --- a/pci.c
> +++ b/pci.c
> @@ -157,6 +157,42 @@ static struct ioport_operations pci_config_data_ops = {
>  	.io_out	= pci_config_data_out,
>  };
>  
> +static void pci_config_command_wr(struct kvm *kvm,
> +				  struct pci_device_header *pci_hdr,
> +				  u16 new_command)
> +{
> +	int i;
> +	bool toggle_io, toggle_mem;
> +
> +	toggle_io = (pci_hdr->command ^ new_command) & PCI_COMMAND_IO;
> +	toggle_mem = (pci_hdr->command ^ new_command) & PCI_COMMAND_MEMORY;
> +
> +	for (i = 0; i < 6; i++) {
> +		if (!pci_bar_is_implemented(pci_hdr, i))
> +			continue;
> +
> +		if (toggle_io && pci__bar_is_io(pci_hdr, i)) {
> +			if (__pci__io_space_enabled(new_command))
> +				pci_hdr->bar_activate_fn(kvm, pci_hdr, i,
> +							 pci_hdr->data);
> +			else
> +				pci_hdr->bar_deactivate_fn(kvm, pci_hdr, i,
> +							   pci_hdr->data);
> +		}
> +
> +		if (toggle_mem && pci__bar_is_memory(pci_hdr, i)) {
> +			if (__pci__memory_space_enabled(new_command))
> +				pci_hdr->bar_activate_fn(kvm, pci_hdr, i,
> +							 pci_hdr->data);
> +			else
> +				pci_hdr->bar_deactivate_fn(kvm, pci_hdr, i,
> +							   pci_hdr->data);
> +		}
> +	}
> +
> +	pci_hdr->command = new_command;
> +}
> +
>  void pci__config_wr(struct kvm *kvm, union pci_config_address addr, void *data, int size)
>  {
>  	void *base;
> @@ -182,6 +218,12 @@ void pci__config_wr(struct kvm *kvm, union pci_config_address addr, void *data,
>  	if (*(u32 *)(base + offset) == 0)
>  		return;
>  
> +	if (offset == PCI_COMMAND) {
> +		memcpy(&value, data, size);
> +		pci_config_command_wr(kvm, pci_hdr, (u16)value);
> +		return;
> +	}
> +
>  	bar = (offset - PCI_BAR_OFFSET(0)) / sizeof(u32);
>  
>  	/*