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

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2012-05-21 at 10:38 +0200, Alexander Graf wrote:
> 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.

I don't understand your question ... this is implemented in qemu...

The problem with SLOF is specific to -M pseries, because it runs in
"guest" real mode, it doesn't have access to device memory unless it
does it via hcalls.

Cheers,
Ben.

> 
> 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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