Re: [RFCv2 07/37] KVM: s390: add new variants of UV CALL

[Thomas Huth <thuth@redhat.com>]

On 03/02/2020 14.19, Christian Borntraeger wrote:
> From: Janosch Frank <frankja@linux.ibm.com>
> 
> This add 2 new variants of the UV CALL.
> 
> The first variant handles UV CALLs that might have longer busy
> conditions or just need longer when doing partial completion. We should
> schedule when necessary.
> 
> The second variant handles UV CALLs that only need the handle but have
> no payload (e.g. destroying a VM). We can provide a simple wrapper for
> those.
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> ---
>  arch/s390/include/asm/uv.h | 58 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)
> 
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index 4eaea95f5c64..3448f12ef57a 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -14,6 +14,7 @@
>  #include <linux/types.h>
>  #include <linux/errno.h>
>  #include <linux/bug.h>
> +#include <linux/sched.h>
>  #include <asm/page.h>
>  #include <asm/gmap.h>
>  
> @@ -92,6 +93,18 @@ struct uv_cb_cfs {
>  	u64 paddr;
>  } __packed __aligned(8);
>  
> +/*
> + * A common UV call struct for the following calls:
> + * Destroy cpu/config
> + * Verify
> + */
> +struct uv_cb_nodata {
> +	struct uv_cb_header header;
> +	u64 reserved08[2];
> +	u64 handle;
> +	u64 reserved20[4];
> +} __packed __aligned(8);
> +
>  struct uv_cb_share {
>  	struct uv_cb_header header;
>  	u64 reserved08[3];
> @@ -99,6 +112,31 @@ struct uv_cb_share {
>  	u64 reserved28;
>  } __packed __aligned(8);
>  
> +/*
> + * Low level uv_call that takes r1 and r2 as parameter and avoids
> + * stalls for long running busy conditions by doing schedule
> + */
> +static inline int uv_call_sched(unsigned long r1, unsigned long r2)
> +{
> +	int cc = 3;
> +
> +	while (cc > 1) {
> +		asm volatile(
> +			"0:	.insn rrf,0xB9A40000,%[r1],%[r2],0,0\n"
> +			"		ipm	%[cc]\n"
> +			"		srl	%[cc],28\n"
> +			: [cc] "=d" (cc)
> +			: [r1] "a" (r1), [r2] "a" (r2)

You could use "d" instead of "a" for both, r1 and r2, here.

> +			: "memory", "cc");
> +		if (need_resched())
> +			schedule();
> +	}

It's a matter of taste, but I'd rather do:

   int cc;
   do {
       ...
   } while (cc > 1);

(i.e. no need to pre-initialize cc with 3)

> +	return cc;
> +}

 Thomas