On Mon, Jul 01, 2019 at 04:19:46PM +1000, Suraj Jitindar Singh wrote: > The ibm,get_system_parameter rtas call is used by the guest to retrieve > data relating to certain parameters of the system. The SPLPAR > characteristics option (token 20) is used to determin characteristics of > the environment in which the lpar will run. > > It may be useful for a guest to know the number of physical host threads > present on the underlying system where it is being run. Add the > characteristic "HostThrs" to the SPLPAR Characteristics > ibm,get_system_parameter rtas call to expose this information to a > guest and provide an implementation which determines this information > based on the number of interrupt servers present in the device tree. > > Signed-off-by: Suraj Jitindar Singh <sjitindarsi...@gmail.com>
Hrm, as I said on our call, I have some misgivings about this.
Starting with the most general: this again publishes host information
to the guest without filtering, which has caused us problems before
(e.g. security issues with publishing the host serial and model
information). Now, I can't immediately see what harm a guest could do
with the host # threads (especially since it could in theory deduce it
from the PVR, I think) but it still makes me uneasy.
Secondly, the "HostThrs" tag doesn't seem to be documented in PAPR as
something that this system-parameter will include. I don't much like
the idea of adding ad-hoc bits of information here without some
thought going into designing and specifying it first.
>
> ---
>
> V1 -> V2:
> - Take into account that the core may be operating in split core mode
> meaning a single core may be split into multiple subcores.
> V2 -> V3:
> - Add curly braces for single line if statements
> ---
> hw/ppc/spapr_rtas.c | 62
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 62 insertions(+)
>
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 5bc1a93271..1bab71c90c 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -229,6 +229,58 @@ static inline int sysparm_st(target_ulong addr,
> target_ulong len,
> return RTAS_OUT_SUCCESS;
> }
>
> +#define CPUS_PATH "/proc/device-tree/cpus/"
> +#define SUBCORE_PATH "/sys/devices/system/cpu/subcores_per_core"
> +
> +static int rtas_get_num_host_threads(void)
> +{
> + int num_threads = -1;
> + unsigned long len;
> + const char *entry;
> + char *buf;
> + GDir *dir;
> +
> + if (!kvm_enabled()) {
> + return 1;
> + }
> +
> + /* Read interrupt servers to determine number of threads per core */
> + dir = g_dir_open(CPUS_PATH, 0, NULL);
> + if (!dir) {
> + return -1;
> + }
> +
> + while ((entry = g_dir_read_name(dir))) {
> + if (!strncmp(entry, "PowerPC,POWER", strlen("PowerPC,POWER"))) {
> + char *path;
> +
> + path = g_strconcat(CPUS_PATH, entry,
> "/ibm,ppc-interrupt-server#s",
> + NULL);
> + if (g_file_get_contents(path, &buf, &len, NULL)) {
> + num_threads = len / sizeof(int);
> + g_free(buf);
> + }
> +
> + g_free(path);
> + break;
> + }
> + }
> +
> + g_dir_close(dir);
> +
> + /* Check if split core mode in use */
> + if (g_file_get_contents(SUBCORE_PATH, &buf, &len, NULL)) {
> + int subcores = g_ascii_strtoll(buf, NULL, 10);
> +
> + if (subcores) {
> + num_threads /= subcores;
> + }
> + g_free(buf);
> + }
Finally, all the logic above is built on the assumption of a ppc host
- and not just that but an IBM POWER host...
> + return num_threads;
> +}
> +
> static void rtas_ibm_get_system_parameter(PowerPCCPU *cpu,
> SpaprMachineState *spapr,
> uint32_t token, uint32_t nargs,
> @@ -250,6 +302,16 @@ static void rtas_ibm_get_system_parameter(PowerPCCPU
> *cpu,
> current_machine->ram_size / MiB,
> smp_cpus,
> max_cpus);
> + int num_host_threads = rtas_get_num_host_threads();
> +
> + if (num_host_threads > 0) {
... this sort of implements a fallback in other cases (KVM PR with a
non-IBM host, TCG, but the boundary conditions are not really well defined.
> + char *hostthr_val, *old = param_val;
> +
> + hostthr_val = g_strdup_printf(",HostThrs=%d", num_host_threads);
> + param_val = g_strconcat(param_val, hostthr_val, NULL);
> + g_free(hostthr_val);
> + g_free(old);
> + }
> ret = sysparm_st(buffer, length, param_val, strlen(param_val) + 1);
> g_free(param_val);
> break;
--
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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