Re: [Qemu-devel] [PATCH 4/4] hw/ppc/spapr: Implement the h_page_init hypercall

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Feb 10, 2016 at 07:09:12PM +0100, Thomas Huth wrote:
> This hypercall either initializes a page with zeros, or copies
> another page.
> According to LoPAPR, the i-cache of the page should also be
> flushed when using H_ICACHE_INVALIDATE or H_ICACHE_SYNCHRONIZE,
> but this is currently only done when running with TCG - assuming
> the cache will be flushed with KVM anyway when switching back to
> kernel / VM context.

I don't think that's true.  dcache and icache aren't usually flushed
by kernel/user or even process context changes in Linux.  Cache
control instructions aren't priveleged so, I think to get this right
you'd need a helper which does dcbst and icbi across the page.

I'm pretty sure libc needs to do this at several points, but alas I
don't think there's an exported function to do it.

> The code currently also does not explicitely flush the data cache
> with H_ICACHE_SYNCHRONIZE, since this either also should be done
> when switching back to kernel / VM context (with KVM), or not matter
> anyway (for TCG).
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  hw/ppc/spapr_hcall.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index f14f849..91e703d 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -387,6 +387,47 @@ static target_ulong h_set_xdabr(PowerPCCPU *cpu, sPAPRMachineState *spapr,
>      return H_SUCCESS;
>  }
>  
> +static target_ulong h_page_init(PowerPCCPU *cpu, sPAPRMachineState *spapr,
> +                                target_ulong opcode, target_ulong *args)
> +{
> +    target_ulong flags = args[0];
> +    target_ulong dest = args[1];
> +    target_ulong src = args[2];
> +    uint8_t buf[TARGET_PAGE_SIZE];
> +
> +    if (flags & ~(H_ICACHE_SYNCHRONIZE | H_ICACHE_INVALIDATE
> +                  | H_COPY_PAGE | H_ZERO_PAGE)) {
> +        qemu_log_mask(LOG_UNIMP, "h_page_init: Bad flags (" TARGET_FMT_lx "\n",
> +                      flags);

This should return H_PARAMETER as well as logging, surely?

> +    }
> +
> +    if (!is_ram_address(spapr, dest) || (dest & ~TARGET_PAGE_MASK) != 0) {
> +        return H_PARAMETER;
> +    }
> +
> +    if (flags & H_COPY_PAGE) {
> +        if (!is_ram_address(spapr, src) || (src & ~TARGET_PAGE_MASK) != 0) {
> +            return H_PARAMETER;
> +        }
> +        cpu_physical_memory_read(src, buf, TARGET_PAGE_SIZE);
> +    } else if (flags & H_ZERO_PAGE) {
> +        memset(buf, 0, TARGET_PAGE_SIZE);
> +    }
> +
> +    if (flags & (H_COPY_PAGE | H_ZERO_PAGE)) {
> +        cpu_physical_memory_write(dest, buf, TARGET_PAGE_SIZE);
> +    }

Hmm, so this does 2 copies for an H_COPY_PAGE and a zero and a copy
for H_ZERO_PAGE, which is going to be substantially slower than the
caller might expect.

> +    if (flags & (H_ICACHE_SYNCHRONIZE | H_ICACHE_INVALIDATE)) {
> +        if (tcg_enabled()) {
> +            tb_flush(CPU(cpu));
> +        }
> +        /* XXX: Flush data cache for H_ICACHE_SYNCHRONIZE? */
> +    }
> +
> +    return H_SUCCESS;
> +}
> +
>  #define FLAGS_REGISTER_VPA         0x0000200000000000ULL
>  #define FLAGS_REGISTER_DTL         0x0000400000000000ULL
>  #define FLAGS_REGISTER_SLBSHADOW   0x0000600000000000ULL
> @@ -1046,6 +1087,7 @@ static void hypercall_register_types(void)
>      spapr_register_hypercall(H_SET_SPRG0, h_set_sprg0);
>      spapr_register_hypercall(H_SET_DABR, h_set_dabr);
>      spapr_register_hypercall(H_SET_XDABR, h_set_xdabr);
> +    spapr_register_hypercall(H_PAGE_INIT, h_page_init);
>      spapr_register_hypercall(H_SET_MODE, h_set_mode);
>  
>      /* "debugger" hcalls (also used by SLOF). Note: We do -not- differenciate

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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