Re: [PATCH] spapr: Add "memop" hypercall

Alexander Graf
2012-05-21T08:38:46Z

On 21.05.2012, at 09:24, Benjamin Herrenschmidt wrote:

> This adds a kvm-specific hypervisor call to the pseries machine
> which allows to do what amounts to memmove, memcpy and xor over
> regions of physical memory such as the framebuffer.
>
> This is the simplest way to get usable framebuffer speed from
> SLOF since the framebuffer isn't mapped in the VRMA and so would
> otherwise require an hcall per 8 bytes access.
>
> The performance is still not great but usable, and can be improved
> with a more complex implementation of the hcall itself if needed.

Shouldn't we try and implement the same thing in QEMU as well to make things compatible? Also, what would the downside be of always going through QEMU for this hypercall?

The reason I'm asking is that we might want to do memmove,memcpy,xor on MMIO memory, which then user space could easily do, but which incurs quite some headaches to do it from inside KVM.

Alex

>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
> hw/spapr.h | 3 ++-
> hw/spapr_hcall.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/hw/spapr.h b/hw/spapr.h
> index 7c497aa..0343f33 100644
> --- a/hw/spapr.h
> +++ b/hw/spapr.h
> @@ -264,7 +264,8 @@ typedef struct sPAPREnvironment {
> */
> #define KVMPPC_HCALL_BASE 0xf000
> #define KVMPPC_H_RTAS (KVMPPC_HCALL_BASE + 0x0)
> -#define KVMPPC_HCALL_MAX KVMPPC_H_RTAS
> +#define KVMPPC_H_LOGICAL_MEMOP (KVMPPC_HCALL_BASE + 0x1)
> +#define KVMPPC_HCALL_MAX KVMPPC_H_LOGICAL_MEMOP
>
> extern sPAPREnvironment *spapr;
>
> diff --git a/hw/spapr_hcall.c b/hw/spapr_hcall.c
> index 94bb504..c5c26dc 100644
> --- a/hw/spapr_hcall.c
> +++ b/hw/spapr_hcall.c
> @@ -608,6 +608,54 @@ static target_ulong h_logical_store(CPUPPCState *env, sPAPREnvironment *spapr,
> return H_PARAMETER;
> }
>
> +static target_ulong h_logical_memop(CPUPPCState *env, sPAPREnvironment *spapr,
> + target_ulong opcode, target_ulong *args)
> +{
> + target_ulong dst = args[0]; /* Destination address */
> + target_ulong src = args[1]; /* Source address */
> + target_ulong esize = args[2]; /* Element size (0=1,1=2,2=4,3=8) */
> + target_ulong count = args[3]; /* Element count */
> + target_ulong op = args[4]; /* 0 = copy, 1 = invert */
> + uint64_t tmp;
> + unsigned int mask = (1 << esize) - 1;
> + int step = 1 << esize;
> +
> + if (count > 0x80000000)
> + return H_PARAMETER;
> +
> + if ((dst & mask) || (src & mask))
> + return H_PARAMETER;
> +
> + if (dst >= src && dst < (src + (count << esize))) {
> + dst = dst + ((count - 1) << esize);
> + src = src + ((count - 1) << esize);
> + step = -step;
> + }
> +
> + while(count--) {
> + switch (esize) {
> + case 0: tmp = ldub_phys(src); break;
> + case 1: tmp = lduw_phys(src); break;
> + case 2: tmp = ldl_phys(src); break;
> + case 3: tmp = ldq_phys(src); break;
> + default:
> + return H_PARAMETER;
> + }
> + if (op)
> + tmp = ~tmp;
> + switch (esize) {
> + case 0: stb_phys(dst, tmp); break;
> + case 1: stw_phys(dst, tmp); break;
> + case 2: stl_phys(dst, tmp); break;
> + case 3: stq_phys(dst, tmp); break;
> + }
> + dst = dst + step;
> + src = src + step;
> + }
> +
> + return H_SUCCESS;
> +}
> +
> static target_ulong h_logical_icbi(CPUPPCState *env, sPAPREnvironment *spapr,
> target_ulong opcode, target_ulong *args)
> {
> @@ -700,6 +748,7 @@ static void hypercall_register_types(void)
> spapr_register_hypercall(H_LOGICAL_CACHE_STORE, h_logical_store);
> spapr_register_hypercall(H_LOGICAL_ICBI, h_logical_icbi);
> spapr_register_hypercall(H_LOGICAL_DCBF, h_logical_dcbf);
> + spapr_register_hypercall(KVMPPC_H_LOGICAL_MEMOP, h_logical_memop);
>
> /* qemu/KVM-PPC specific hcalls */
> spapr_register_hypercall(KVMPPC_H_RTAS, h_rtas);
>
>
> --
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