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

On 8 Feb 2023, at 21:06, Mitchell Horne <mhorne@freebsd.org> wrote:
> 
> 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?

The commit message just doesn’t make sense to me, it switches between
talking about I/O space and memory (same applies to the comments in the
code). Is this reserving I/O parts of the address space so
SYS_RES_MEMORY doesn’t include them (which doesn’t *belong* to physical
memory, just resides in the same address space), reserving
FDT/ACPI-reserved actual RAM memory regions so SYS_RES_MEMORY doesn’t
include them (which isn’t I/O space), or both? Currently it reads to me
as describing part of one and part of the other, but neither fully.

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 */