[RFC PATCH 03/14] RISC-V: paravirt: Implement steal-time support

[Guo Ren <guoren@kernel.org>]

On Wed, Apr 19, 2023 at 10:42:16AM +0200, Andrew Jones wrote:
> On Mon, Apr 17, 2023 at 12:33:51PM +0200, Andrew Jones wrote:
> > When the SBI STA extension exists we can use it to implement
> > paravirt steal-time support. Fill in the empty pv-time functions
> > with an SBI STA implementation.
> > 
> > Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> > ---
> >  arch/riscv/kernel/paravirt.c | 56 ++++++++++++++++++++++++++++++++++--
> >  1 file changed, 53 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/riscv/kernel/paravirt.c b/arch/riscv/kernel/paravirt.c
> > index 141dbcc36fa2..5f8d96b919e4 100644
> > --- a/arch/riscv/kernel/paravirt.c
> > +++ b/arch/riscv/kernel/paravirt.c
> > @@ -6,12 +6,21 @@
> >  #define pr_fmt(fmt) "riscv-pv: " fmt
> >  
> >  #include <linux/cpuhotplug.h>
> > +#include <linux/compiler.h>
> > +#include <linux/errno.h>
> >  #include <linux/init.h>
> >  #include <linux/jump_label.h>
> > +#include <linux/kconfig.h>
> > +#include <linux/kernel.h>
> > +#include <linux/percpu-defs.h>
> >  #include <linux/printk.h>
> >  #include <linux/static_call.h>
> >  #include <linux/types.h>
> >  
> > +#include <asm/barrier.h>
> > +#include <asm/page.h>
> > +#include <asm/sbi.h>
> > +
> >  struct static_key paravirt_steal_enabled;
> >  struct static_key paravirt_steal_rq_enabled;
> >  
> > @@ -31,24 +40,65 @@ static int __init parse_no_stealacc(char *arg)
> >  
> >  early_param("no-steal-acc", parse_no_stealacc);
> >  
> > +DEFINE_PER_CPU(struct sbi_sta_struct, steal_time) __aligned(64);
> > +
> >  static bool __init has_pv_steal_clock(void)
> >  {
> > +	if (sbi_probe_extension(SBI_EXT_STA) > 0) {
> > +		pr_info("SBI STA extension detected\n");
> > +		return true;
> > +	}
> > +
> >  	return false;
> >  }
> >  
> > -static int pv_time_cpu_online(unsigned int cpu)
> > +static int sbi_sta_set_steal_time_shmem(unsigned long lo, unsigned long hi,
> > +					unsigned long flags)
> >  {
> > +	struct sbiret ret;
> > +
> > +	ret = sbi_ecall(SBI_EXT_STA, SBI_EXT_STA_SET_STEAL_TIME_SHMEM,
> > +			lo, hi, flags, 0, 0, 0);
> > +	if (ret.error) {
> > +		if (lo == -1 && hi == -1)
> > +			pr_warn("Failed to disable steal-time shmem");
> > +		else
> > +			pr_warn("Failed to set steal-time shmem");
> > +		return -ENOMEM;
> > +	}
> > +
> >  	return 0;
> >  }
> >  
> > +static int pv_time_cpu_online(unsigned int cpu)
> > +{
> > +	struct sbi_sta_struct *st = this_cpu_ptr(&steal_time);
> > +	phys_addr_t pa = __pa(st);
> > +	unsigned long lo = (unsigned long)pa;
> > +	unsigned long hi = IS_ENABLED(CONFIG_32BIT) ? upper_32_bits((u64)pa) : 0;
> > +
> > +	return sbi_sta_set_steal_time_shmem(lo, hi, 0);
> > +}
> > +
> >  static int pv_time_cpu_down_prepare(unsigned int cpu)
> >  {
> > -	return 0;
> > +	return sbi_sta_set_steal_time_shmem(-1, -1, 0);
> >  }
> >  
> >  static u64 pv_time_steal_clock(int cpu)
> >  {
> > -	return 0;
> > +	struct sbi_sta_struct *st = per_cpu_ptr(&steal_time, cpu);
> > +	u32 sequence;
> > +	u64 steal;
> > +
> > +	do {
> > +		sequence = st->sequence;
> > +		virt_rmb();
> > +		steal = st->steal;
> > +		virt_rmb();
> > +	} while ((sequence & 1) || (sequence != st->sequence));
> > +
> > +	return steal;
> >  }
> 
> So anybody poking around the implementations for other architectures will
> see that I shamelessly ripped this off from x86's implementation. However,
> looking at it again, I think all the references to the steal-time info
> should be wrapped in READ_ONCE(). I'll write a patch for x86/kvm to
> add READ_ONCE's and also update this patch for rfc-v2.
Hello, what's the status of rfc-v2? The riscv paravirt_qspinlock is
based on your series to reuse the paravirt.c and CONFIG_PARAVIRT.

https://lore.kernel.org/linux-riscv/20230802164701.192791-10-guoren at kernel.org/
https://lore.kernel.org/linux-riscv/20230802164701.192791-17-guoren at kernel.org/

> 
> Thanks,
> drew
> 
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