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Wed, 23 Dec 2020 20:58:41 +0000 (GMT) Date: Wed, 23 Dec 2020 12:58:38 -0800 From: Ram Pai To: Thiago Jung Bauermann Subject: Re: [PATCH] powerpc/mm: Limit allocation of SWIOTLB on server machines Message-ID: <20201223205838.GA4102@ram-ibm-com.ibm.com> References: <20201218062103.76102-1-bauerman@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201218062103.76102-1-bauerman@linux.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.343, 18.0.737 definitions=2020-12-23_10:2020-12-23, 2020-12-23 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 malwarescore=0 impostorscore=0 suspectscore=0 clxscore=1011 mlxscore=0 spamscore=0 priorityscore=1501 mlxlogscore=999 bulkscore=0 lowpriorityscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2012230143 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Ram Pai Cc: Satheesh Rajendran , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Fri, Dec 18, 2020 at 03:21:03AM -0300, Thiago Jung Bauermann wrote: > On server-class POWER machines, we don't need the SWIOTLB unless we're a > secure VM. Nevertheless, if CONFIG_SWIOTLB is enabled we unconditionally > allocate it. > > In most cases this is harmless, but on a few machine configurations (e.g., > POWER9 powernv systems with 4 GB area reserved for crashdump kernel) it can > happen that memblock can't find a 64 MB chunk of memory for the SWIOTLB and > fails with a scary-looking WARN_ONCE: > > ------------[ cut here ]------------ > memblock: bottom-up allocation failed, memory hotremove may be affected > WARNING: CPU: 0 PID: 0 at mm/memblock.c:332 memblock_find_in_range_node+0x328/0x340 > Modules linked in: > CPU: 0 PID: 0 Comm: swapper Not tainted 5.10.0-rc2-orig+ #6 > NIP: c000000000442f38 LR: c000000000442f34 CTR: c0000000001e0080 > REGS: c000000001def900 TRAP: 0700 Not tainted (5.10.0-rc2-orig+) > MSR: 9000000002021033 CR: 28022222 XER: 20040000 > CFAR: c00000000014b7b4 IRQMASK: 1 > GPR00: c000000000442f34 c000000001defba0 c000000001deff00 0000000000000047 > GPR04: 00000000ffff7fff c000000001def828 c000000001def820 0000000000000000 > GPR08: 0000001ffc3e0000 c000000001b75478 c000000001b75478 0000000000000001 > GPR12: 0000000000002000 c000000002030000 0000000000000000 0000000000000000 > GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000002030000 > GPR20: 0000000000000000 0000000000010000 0000000000010000 c000000001defc10 > GPR24: c000000001defc08 c000000001c91868 c000000001defc18 c000000001c91890 > GPR28: 0000000000000000 ffffffffffffffff 0000000004000000 00000000ffffffff > NIP [c000000000442f38] memblock_find_in_range_node+0x328/0x340 > LR [c000000000442f34] memblock_find_in_range_node+0x324/0x340 > Call Trace: > [c000000001defba0] [c000000000442f34] memblock_find_in_range_node+0x324/0x340 (unreliable) > [c000000001defc90] [c0000000015ac088] memblock_alloc_range_nid+0xec/0x1b0 > [c000000001defd40] [c0000000015ac1f8] memblock_alloc_internal+0xac/0x110 > [c000000001defda0] [c0000000015ac4d0] memblock_alloc_try_nid+0x94/0xcc > [c000000001defe30] [c00000000159c3c8] swiotlb_init+0x78/0x104 > [c000000001defea0] [c00000000158378c] mem_init+0x4c/0x98 > [c000000001defec0] [c00000000157457c] start_kernel+0x714/0xac8 > [c000000001deff90] [c00000000000d244] start_here_common+0x1c/0x58 > Instruction dump: > 2c230000 4182ffd4 ea610088 ea810090 4bfffe84 39200001 3d42fff4 3c62ff60 > 3863c560 992a8bfc 4bd0881d 60000000 <0fe00000> ea610088 4bfffd94 60000000 > random: get_random_bytes called from __warn+0x128/0x184 with crng_init=0 > ---[ end trace 0000000000000000 ]--- > software IO TLB: Cannot allocate buffer > > Unless this is a secure VM the message can actually be ignored, because the > SWIOTLB isn't needed. Therefore, let's avoid the SWIOTLB in those cases. The above warn_on is conveying a genuine warning. Should it be silenced? > > Fixes: eae9eec476d1 ("powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory") > Signed-off-by: Thiago Jung Bauermann > --- > arch/powerpc/mm/mem.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c > index afab328d0887..3af991844145 100644 > --- a/arch/powerpc/mm/mem.c > +++ b/arch/powerpc/mm/mem.c > @@ -300,7 +300,8 @@ void __init mem_init(void) > memblock_set_bottom_up(true); > if (is_secure_guest()) > svm_swiotlb_init(); > - else > + /* Server machines don't need SWIOTLB if they're not secure guests. */ > + else if (!machine_is(pseries) && !machine_is(powernv)) I can see powernv never needing SWIOTLB. But, pseries guests, I am not so sure. RP