[kvm-unit-tests v2 03/10] powerpc: abstract H_CEDE calls into a sleep functions

[Thomas Huth]

On 20/03/2023 08.03, Nicholas Piggin wrote:
> This consolidates several implementations, and it no longer leaves
> MSR[EE] enabled after the decrementer interrupt is handled, but
> rather disables it on return.
> 
> The handler no longer allows a continuous ticking, but rather dec
> has to be re-armed and EE re-enabled (e.g., via H_CEDE hcall) each
> time.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   lib/powerpc/asm/handlers.h  |  2 +-
>   lib/powerpc/asm/ppc_asm.h   |  1 +
>   lib/powerpc/asm/processor.h |  7 +++++++
>   lib/powerpc/handlers.c      | 10 ++++-----
>   lib/powerpc/processor.c     | 42 +++++++++++++++++++++++++++++++++++++
>   powerpc/sprs.c              |  6 +-----
>   powerpc/tm.c                | 20 +-----------------
>   7 files changed, 57 insertions(+), 31 deletions(-)
> 
> diff --git a/lib/powerpc/asm/handlers.h b/lib/powerpc/asm/handlers.h
> index 64ba727..e4a0cd4 100644
> --- a/lib/powerpc/asm/handlers.h
> +++ b/lib/powerpc/asm/handlers.h
> @@ -3,6 +3,6 @@
>   
>   #include <asm/ptrace.h>
>   
> -void dec_except_handler(struct pt_regs *regs, void *data);
> +void dec_handler_oneshot(struct pt_regs *regs, void *data);
>   
>   #endif /* _ASMPOWERPC_HANDLERS_H_ */
> diff --git a/lib/powerpc/asm/ppc_asm.h b/lib/powerpc/asm/ppc_asm.h
> index 1b85f6b..6299ff5 100644
> --- a/lib/powerpc/asm/ppc_asm.h
> +++ b/lib/powerpc/asm/ppc_asm.h
> @@ -36,6 +36,7 @@
>   #endif /* __BYTE_ORDER__ */
>   
>   /* Machine State Register definitions: */
> +#define MSR_EE_BIT	15			/* External Interrupts Enable */
>   #define MSR_SF_BIT	63			/* 64-bit mode */
>   
>   #endif /* _ASMPOWERPC_PPC_ASM_H */
> diff --git a/lib/powerpc/asm/processor.h b/lib/powerpc/asm/processor.h
> index ac001e1..ebfeff2 100644
> --- a/lib/powerpc/asm/processor.h
> +++ b/lib/powerpc/asm/processor.h
> @@ -20,6 +20,8 @@ static inline uint64_t get_tb(void)
>   
>   extern void delay(uint64_t cycles);
>   extern void udelay(uint64_t us);
> +extern void sleep_tb(uint64_t cycles);
> +extern void usleep(uint64_t us);
>   
>   static inline void mdelay(uint64_t ms)
>   {
> @@ -27,4 +29,9 @@ static inline void mdelay(uint64_t ms)
>   		udelay(1000);
>   }
>   
> +static inline void msleep(uint64_t ms)
> +{
> +	usleep(ms * 1000);
> +}
> +
>   #endif /* _ASMPOWERPC_PROCESSOR_H_ */
> diff --git a/lib/powerpc/handlers.c b/lib/powerpc/handlers.c
> index c8721e0..296f14f 100644
> --- a/lib/powerpc/handlers.c
> +++ b/lib/powerpc/handlers.c
> @@ -9,15 +9,13 @@
>   #include <libcflat.h>
>   #include <asm/handlers.h>
>   #include <asm/ptrace.h>
> +#include <asm/ppc_asm.h>
>   
>   /*
>    * Generic handler for decrementer exceptions (0x900)
> - * Just reset the decrementer back to the value specified when registering the
> - * handler
> + * Return with MSR[EE] disabled.
>    */
> -void dec_except_handler(struct pt_regs *regs __unused, void *data)
> +void dec_handler_oneshot(struct pt_regs *regs, void *data)
>   {
> -	uint64_t dec = *((uint64_t *) data);
> -
> -	asm volatile ("mtdec %0" : : "r" (dec));
> +	regs->msr &= ~(1UL << MSR_EE_BIT);
>   }
> diff --git a/lib/powerpc/processor.c b/lib/powerpc/processor.c
> index ec85b9d..e77a240 100644
> --- a/lib/powerpc/processor.c
> +++ b/lib/powerpc/processor.c
> @@ -10,6 +10,8 @@
>   #include <asm/ptrace.h>
>   #include <asm/setup.h>
>   #include <asm/barrier.h>
> +#include <asm/hcall.h>
> +#include <asm/handlers.h>
>   
>   static struct {
>   	void (*func)(struct pt_regs *, void *data);
> @@ -54,3 +56,43 @@ void udelay(uint64_t us)
>   {
>   	delay((us * tb_hz) / 1000000);
>   }
> +
> +void sleep_tb(uint64_t cycles)
> +{
> +	uint64_t start, end, now;
> +
> +	start = now = get_tb();
> +	end = start + cycles;
> +
> +	while (end > now) {
> +		uint64_t left = end - now;
> +
> +		/* Could support large decrementer */
> +		if (left > 0x7fffffff)
> +			left = 0x7fffffff;
> +
> +		asm volatile ("mtdec %0" : : "r" (left));
> +		handle_exception(0x900, &dec_handler_oneshot, NULL);

Wouldn't it be better to first call handle_exception() before moving 
something into the decrementer?

> +		/*
> +		 * H_CEDE is called with MSR[EE] clear and enables it as part
> +		 * of the hcall, returning with EE enabled. The dec interrupt
> +		 * is then taken immediately and the handler disables EE.
> +		 *
> +		 * If H_CEDE returned for any other interrupt than dec
> +		 * expiring, that is considered an unhandled interrupt and
> +		 * the test case would be stopped.
> +		 */
> +		if (hcall(H_CEDE) != H_SUCCESS) {
> +			printf("H_CEDE failed\n");
> +			abort();
> +		}
> +		handle_exception(0x900, NULL, NULL);
> +
> +		now = get_tb();
> +	}
> +}

  Thomas