Re: git: e6cf1a0826c9 - main - physmem: add ram0 pseudo-driver

On 8 Feb 2023, at 20:52, Mitchell Horne <mhorne@FreeBSD.org> wrote:
> 
> The branch main has been updated by mhorne:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=e6cf1a0826c9d7f229e41224ec7b783501636528
> 
> commit e6cf1a0826c9d7f229e41224ec7b783501636528
> Author:     Mitchell Horne <mhorne@FreeBSD.org>
> AuthorDate: 2021-05-27 14:27:40 +0000
> Commit:     Mitchell Horne <mhorne@FreeBSD.org>
> CommitDate: 2023-02-08 20:50:46 +0000
> 
>    physmem: add ram0 pseudo-driver
> 
>    Its purpose is to reserve all I/O space belonging to physical memory

If it’s RAM then it’s not I/O, and if it’s I/O then it’s not RAM?

Jess

>    from nexus, preventing it from being handed out by bus_alloc_resource()
>    to callers such as xenpv_alloc_physmem(), which looks for the first
>    available free range it can get. This mimics the existing pseudo-driver
>    on x86.
> 
>    If needed, the device can be disabled with hint.ram.0.disabled="1" in
>    /boot/device.hints.
> 
>    Reviewed by:    imp
>    MFC after:      1 month
>    Differential Revision:  https://reviews.freebsd.org/D32343
> ---
> sys/kern/subr_physmem.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 99 insertions(+), 1 deletion(-)
> 
> diff --git a/sys/kern/subr_physmem.c b/sys/kern/subr_physmem.c
> index 498ad2440f40..bb6af5a580aa 100644
> --- a/sys/kern/subr_physmem.c
> +++ b/sys/kern/subr_physmem.c
> @@ -40,7 +40,9 @@ __FBSDID("$FreeBSD$");
> 
> #include <sys/param.h>
> #include <sys/systm.h>
> +#include <sys/bus.h>
> #include <sys/kernel.h>
> +#include <sys/module.h>
> #include <sys/physmem.h>
> 
> #ifdef _KERNEL
> @@ -49,7 +51,9 @@ __FBSDID("$FreeBSD$");
> #include <vm/vm_page.h>
> #include <vm/vm_phys.h>
> #include <vm/vm_dumpset.h>
> +
> #include <machine/md_var.h>
> +#include <machine/resource.h>
> #else
> #include <stdarg.h>
> #include <stdio.h>
> @@ -524,7 +528,6 @@ physmem_init_kernel_globals(void)
> 		panic("No memory entries in phys_avail");
> 	Maxmem = atop(phys_avail[nextidx - 1]);
> }
> -#endif
> 
> #ifdef DDB
> #include <ddb/ddb.h>
> @@ -536,3 +539,98 @@ DB_SHOW_COMMAND_FLAGS(physmem, db_show_physmem, DB_CMD_MEMSAFE)
> }
> 
> #endif /* DDB */
> +
> +/*
> + * ram pseudo driver - this reserves I/O space resources corresponding to physical
> + * memory regions.
> + */
> +
> +static void
> +ram_identify(driver_t *driver, device_t parent)
> +{
> +
> +	if (resource_disabled("ram", 0))
> +		return;
> +	if (BUS_ADD_CHILD(parent, 0, "ram", 0) == NULL)
> +		panic("ram_identify");
> +}
> +
> +static int
> +ram_probe(device_t dev)
> +{
> +
> +	device_quiet(dev);
> +	device_set_desc(dev, "System RAM");
> +	return (BUS_PROBE_SPECIFIC);
> +}
> +
> +static int
> +ram_attach(device_t dev)
> +{
> +	vm_paddr_t avail_list[PHYS_AVAIL_COUNT];
> +	rman_res_t start, end;
> +	struct region *hwp;
> +	int rid, i;
> +
> +	rid = 0;
> +
> +	/* Get the avail list. */
> +	bzero(avail_list, sizeof(avail_list));
> +	regions_to_avail(avail_list, EXFLAG_NOALLOC | EXFLAG_NODUMP,
> +	    PHYS_AVAIL_COUNT, 0, NULL, NULL);
> +
> +	/* Reserve all memory regions. */
> +	for (i = 0; avail_list[i + 1] != 0; i += 2) {
> +		start = avail_list[i];
> +		end = avail_list[i + 1];
> +
> +		if (bootverbose)
> +			device_printf(dev,
> +			    "reserving memory region:   %jx-%jx\n",
> +			    (uintmax_t)start, (uintmax_t)end);
> +
> +		if (bus_alloc_resource(dev, SYS_RES_MEMORY, &rid, start, end,
> +		    end - start, 0) == NULL)
> +			panic("ram_attach: resource %d failed to attach", rid);
> +		rid++;
> +	}
> +
> +	/* Now, reserve the excluded memory regions. */
> +	for (i = 0, hwp = exregions; i < excnt; i++, hwp++) {
> +		start = hwp->addr;
> +		end = hwp->addr + hwp->size;
> +
> +		if (bootverbose)
> +			device_printf(dev,
> +			    "reserving excluded region: %jx-%jx\n",
> +			    (uintmax_t)start, (uintmax_t)(end - 1));
> +
> +		/*
> +		 * Best-effort attempt to reserve the range. This may fail, as
> +		 * sometimes the excluded ranges provided by the device tree
> +		 * will cover or overlap some I/O range.
> +		 */
> +		if (bus_alloc_resource(dev, SYS_RES_MEMORY, &rid, start, end,
> +		    end - start, 0) == NULL) {
> +			if (bootverbose)
> +				device_printf(dev, "failed to reserve region\n");
> +			continue;
> +		}
> +		rid++;
> +	}
> +
> +	return (0);
> +}
> +
> +static device_method_t ram_methods[] = {
> +	/* Device interface */
> +	DEVMETHOD(device_identify,	ram_identify),
> +	DEVMETHOD(device_probe,		ram_probe),
> +	DEVMETHOD(device_attach,	ram_attach),
> +
> +	DEVMETHOD_END
> +};
> +
> +DEFINE_CLASS_0(ram, ram_driver, ram_methods, /* no softc */ 1);
> +DRIVER_MODULE(ram, nexus, ram_driver, 0, 0);
> +#endif /* _KERNEL */