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

On 2/8/23 16:55, Jessica Clarke wrote:
> 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
> 

Yes, they are distinct. And yet, they share an address space. So this is 
to assist in the SYS_RES_MEMORY resource bookkeeping. Did I misuse some 
terminology, or what is your actual question?

>>     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 */
>