[SeaBIOS] [PATCH v2] config: Add function to check if fw_cfg exists

[Laszlo Ersek]

On 03/15/17 00:09, Petr Berky wrote:
> From b06589c683a7defb4853a3b810bd7e6a12abe2d6 Mon Sep 17 00:00:00 2001
> From: Petr Berky <petr.berky at email.cz>
> Date: Tue, 14 Mar 2017 23:32:15 +0100
> Subject: [PATCH v2] config: Add function to check if fw_cfg exists
> 
> It was found qemu_get_present_cpus_count may return impossible
> number of cpus because of not checking if fw_cfg exists before
> using it. That  may lead to undefined behavior of emulator,
> in particular Bochs that freezes.
> 
> Signed-off-by: Petr Berky <petr.berky at email.cz>
> ---
>  src/fw/paravirt.c | 12 +++++++++++-
>  src/fw/paravirt.h |  1 +
>  2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/src/fw/paravirt.c b/src/fw/paravirt.c
> index 707502d..dfc69d4 100644
> --- a/src/fw/paravirt.c
> +++ b/src/fw/paravirt.c
> @@ -32,9 +32,16 @@ u32 RamSize;
>  u64 RamSizeOver4G;
>  // Type of emulator platform.
>  int PlatformRunningOn VARFSEG;
> +// cfg enabled
> +int cfg_enabled = 0;
>  // cfg_dma enabled
>  int cfg_dma_enabled = 0;
> 
> +inline int qemu_cfg_enabled(void)
> +{
> +    return cfg_enabled;
> +}
> +
>  inline int qemu_cfg_dma_enabled(void)
>  {
>      return cfg_dma_enabled;
> @@ -392,7 +399,9 @@ u16
>  qemu_get_present_cpus_count(void)
>  {
>      u16 smp_count = 0;
> -    qemu_cfg_read_entry(&smp_count, QEMU_CFG_NB_CPUS, sizeof(smp_count));
> +    if (qemu_cfg_enabled()) {
> +        qemu_cfg_read_entry(&smp_count, QEMU_CFG_NB_CPUS,
> sizeof(smp_count));
> +    }
>      u16 cmos_cpu_count = rtc_read(CMOS_BIOS_SMP_COUNT) + 1;
>      if (smp_count < cmos_cpu_count) {
>          smp_count = cmos_cpu_count;
> @@ -570,6 +579,7 @@ void qemu_cfg_init(void)
>          if (inb(PORT_QEMU_CFG_DATA) != sig[i])
>              return;
> 
> +    cfg_enabled = 1;
>      dprintf(1, "Found QEMU fw_cfg\n");
> 
>      // Detect DMA interface.

If we wanted to parallel the DMA check 100%, we'd set the variable under
the debug message, not above it, but even I am not that pedantic. :)

Reviewed-by: Laszlo Ersek <lersek at redhat.com>

Igor, can you check if this is safe for S3 resume too? I think it is,
but I had better ask you.

Thanks
Laszlo


> diff --git a/src/fw/paravirt.h b/src/fw/paravirt.h
> index 16f3d9a..a14d83e 100644
> --- a/src/fw/paravirt.h
> +++ b/src/fw/paravirt.h
> @@ -49,6 +49,7 @@ static inline int runningOnKVM(void) {
>  // QEMU_CFG_DMA ID bit
>  #define QEMU_CFG_VERSION_DMA    2
> 
> +int qemu_cfg_enabled(void);
>  int qemu_cfg_dma_enabled(void);
>  void qemu_preinit(void);
>  void qemu_platform_setup(void);