Date: Wed, 8 Feb 2023 18:26:25 -0400 From: Mitchell Horne <mhorne@freebsd.org> To: Jessica Clarke <jrtc27@freebsd.org> Cc: "src-committers@freebsd.org" <src-committers@FreeBSD.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@FreeBSD.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@FreeBSD.org> Subject: Re: git: e6cf1a0826c9 - main - physmem: add ram0 pseudo-driver Message-ID: <5cfc2de7-4b08-283b-b9fc-c990f236ff3e@freebsd.org> In-Reply-To: <505D72C8-1F67-46C8-A6EF-39392841FBF5@freebsd.org> References: <202302082052.318KqOE6052473@gitrepo.freebsd.org> <26339898-C02C-42D4-916A-2B6AD2562B02@freebsd.org> <d2156648-6181-6721-12e3-dae5ae15e49c@freebsd.org> <505D72C8-1F67-46C8-A6EF-39392841FBF5@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On 2/8/23 17:13, Jessica Clarke wrote: > 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 Okay sure, perhaps the term I am searching for but missing is "physical address space". We know that some regions of physical address space correspond to RAM/memory/"physical memory". Other portions of the address space correspond to memory-mapped I/O regions belonging to one or more devices. Device drivers allocate SYS_RES_MEMORY resources using e.g. bus_alloc_resource(). They do this to declare ownership of the particular range of physical address space that they will use for I/O. If it's not RF_SHAREABLE, then it can't be handed out again. Memory/RAM is handed out by a different set of APIs, and therefore never touches SYS_RES_MEMORY resources. However, it is true that the (tangible) physical memory in the system maps to a set of regions in the (abstract) physical address space. This is the sense in which I used the word "belong". The purpose of the change is to reserve, from the system-wide SYS_RES_MEMORY rman, those portions of the physical address space that correspond to real physical memory/RAM. > >>>> 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 */ >
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?5cfc2de7-4b08-283b-b9fc-c990f236ff3e>