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mbuf: Only allow extpg mbufs if the system has a direct map

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Some upcoming changes will modify software checksum routines like
in_cksum() to operate using m_apply(), which uses the direct map to
access packet data for unmapped mbufs.  This approach of course does not
work on platforms without a direct map, so we have to disallow the use
of unmapped mbufs on such platforms.

I believe this is the right tradeoff: we only configure KTLS on amd64
and arm64 today (and one KTLS consumer, NFS TLS, requires a direct map
already), and the use of unmapped mbufs with plain sendfile is a recent
optimization.  If need be, m_apply() could be modified to create
CPU-private mappings of extpg mbuf pages as a fallback.

So, change mb_use_ext_pgs to be hard-wired to zero on systems without a
direct map.  Note that PMAP_HAS_DMAP is not a compile-time constant on
some systems, so the default value of mb_use_ext_pgs has to be
determined during boot.

Reviewed by:	jhb
Discussed with:	gallatin
MFC after:	2 weeks
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D32940
This commit is contained in:
Mark Johnston 2021-11-16 13:31:04 -05:00
parent 42188bb5c1
commit fcaa890c44
2 changed files with 31 additions and 3 deletions
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32
sys/kern/kern_mbuf.c
View File

@ -116,9 +116,26 @@ int nmbjumbop; /* limits number of page size jumbo clusters */
int nmbjumbo9; /* limits number of 9k jumbo clusters */
int nmbjumbo16; /* limits number of 16k jumbo clusters */
bool mb_use_ext_pgs = true; /* use M_EXTPG mbufs for sendfile & TLS */
SYSCTL_BOOL(_kern_ipc, OID_AUTO, mb_use_ext_pgs, CTLFLAG_RWTUN,
bool mb_use_ext_pgs = false; /* use M_EXTPG mbufs for sendfile & TLS */
static int
sysctl_mb_use_ext_pgs(SYSCTL_HANDLER_ARGS)
{
int error, extpg;
extpg = mb_use_ext_pgs;
error = sysctl_handle_int(oidp, &extpg, 0, req);
if (error == 0 && req->newptr != NULL) {
if (extpg != 0 && !PMAP_HAS_DMAP)
error = EOPNOTSUPP;
else
mb_use_ext_pgs = extpg != 0;
}
return (error);
}
SYSCTL_PROC(_kern_ipc, OID_AUTO, mb_use_ext_pgs, CTLTYPE_INT | CTLFLAG_RW,
&mb_use_ext_pgs, 0,
sysctl_mb_use_ext_pgs, "IU",
"Use unmapped mbufs for sendfile(2) and TLS offload");
static quad_t maxmbufmem; /* overall real memory limit for all mbufs */
@ -137,6 +154,7 @@ static void
tunable_mbinit(void *dummy)
{
quad_t realmem;
int extpg;
/*
* The default limit for all mbuf related memory is 1/2 of all
@ -173,6 +191,16 @@ tunable_mbinit(void *dummy)
if (nmbufs < nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16)
nmbufs = lmax(maxmbufmem / MSIZE / 5,
nmbclusters + nmbjumbop + nmbjumbo9 + nmbjumbo16);
/*
* Unmapped mbufs can only safely be used on platforms with a direct
* map.
*/
if (PMAP_HAS_DMAP) {
extpg = mb_use_ext_pgs;
TUNABLE_INT_FETCH("kern.ipc.mb_use_ext_pgs", &extpg);
mb_use_ext_pgs = extpg != 0;
}
}
SYSINIT(tunable_mbinit, SI_SUB_KMEM, SI_ORDER_MIDDLE, tunable_mbinit, NULL);

2
sys/rpc/rpcsec_tls/rpctls_impl.c
View File

@ -711,7 +711,7 @@ rpctls_getinfo(u_int *maxlenp, bool rpctlscd_run, bool rpctlssd_run)
int error;
size_t siz;
if (PMAP_HAS_DMAP == 0 || !mb_use_ext_pgs)
if (!mb_use_ext_pgs)
return (false);
siz = sizeof(enable);
error = kernel_sysctlbyname(curthread, "kern.ipc.tls.enable",