Re: [PATCH] ALSA: intel8x0: Drop superfluous VM checks

[Konstantin Ozerkov <kozerkov@parallels.com>]

Ack

On 05/04/16 17:53, Takashi Iwai wrote:
> intel8x0 driver has the inside_vm check for skipping a buggy hardware
> workaround in the PCM pointer callback in the commit [228cf79376f1:
> ALSA: intel8x0: Improve performance in virtual environment].  This was
> originally applied to all devices on known VMs, but the code was
> switched to use the PCI  ID matching for applying to only known
> devices (KVM and Parallels), in order to avoid applying wrongly to
> VT-d and other such cases, in the commit [7fb4f392bd27: ALSA:
> intel8x0: improve virtual environment detection].
>
> Meanwhile, the original VM check was kept even after switching to the
> PCI ID matching.  It was partly because we weren't 100% sure whether
> we had covered all well, and partly because this would help
> identifying the issue once when a user of another VM hit the same
> problem or a regression.  Currently the VM check is used only for
> showing the kernel message that the VM-optimization isn't applied, and
> the VM check itself doesn't change the actual driver behavior at all.
>
> Despite the relatively safe driver behavior, the code caught attention
> of developers badly and brought many confusion / misunderstanding.
> Since we've got neither regression nor enhancement report for other
> VMs for five years long, it's likely safe to drop this superfluous VM
> check now.
>
> The module option is still kept, so if a user still needs to adjust,
> it can be applied as was.
>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Luis R. Rodriguez <mcgrof@kernel.org>
> Cc: Konstantin Ozerkov <kozerkov@parallels.com>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
>   sound/pci/intel8x0.c | 20 +++-----------------
>   1 file changed, 3 insertions(+), 17 deletions(-)
>
> diff --git a/sound/pci/intel8x0.c b/sound/pci/intel8x0.c
> index 8151318a69a2..9720a30dbfff 100644
> --- a/sound/pci/intel8x0.c
> +++ b/sound/pci/intel8x0.c
> @@ -42,12 +42,6 @@
>   #include <asm/pgtable.h>
>   #include <asm/cacheflush.h>
>   
> -#ifdef CONFIG_KVM_GUEST
> -#include <linux/kvm_para.h>
> -#else
> -#define kvm_para_available() (0)
> -#endif
> -
>   MODULE_AUTHOR("Jaroslav Kysela <perex@perex.cz>");
>   MODULE_DESCRIPTION("Intel 82801AA,82901AB,i810,i820,i830,i840,i845,MX440; SiS 7012; Ali 5455");
>   MODULE_LICENSE("GPL");
> @@ -2972,25 +2966,17 @@ static int snd_intel8x0_inside_vm(struct pci_dev *pci)
>   		goto fini;
>   	}
>   
> -	/* detect KVM and Parallels virtual environments */
> -	result = kvm_para_available();
> -#ifdef X86_FEATURE_HYPERVISOR
> -	result = result || boot_cpu_has(X86_FEATURE_HYPERVISOR);
> -#endif
> -	if (!result)
> -		goto fini;
> -
>   	/* check for known (emulated) devices */
> +	result = 0;
>   	if (pci->subsystem_vendor == PCI_SUBVENDOR_ID_REDHAT_QUMRANET &&
>   	    pci->subsystem_device == PCI_SUBDEVICE_ID_QEMU) {
>   		/* KVM emulated sound, PCI SSID: 1af4:1100 */
>   		msg = "enable KVM";
> +		result = 1;
>   	} else if (pci->subsystem_vendor == 0x1ab8) {
>   		/* Parallels VM emulated sound, PCI SSID: 1ab8:xxxx */
>   		msg = "enable Parallels VM";
> -	} else {
> -		msg = "disable (unknown or VT-d) VM";
> -		result = 0;
> +		result = 1;
>   	}
>   
>   fini: