From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id BC3CF1A089D for ; Thu, 27 Nov 2014 10:39:37 +1100 (AEDT) Message-ID: <1417045163.5089.67.camel@kernel.crashing.org> Subject: Re: [PATCH REPOST 3/3] powerpc/vphn: move endianness fixing to vphn_unpack_associativity() From: Benjamin Herrenschmidt To: Greg Kurz Date: Thu, 27 Nov 2014 10:39:23 +1100 In-Reply-To: <20141117174244.7717.83028.stgit@bahia.local> References: <20141117174216.7717.10926.stgit@bahia.local> <20141117174244.7717.83028.stgit@bahia.local> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2014-11-17 at 18:42 +0100, Greg Kurz wrote: > The first argument to vphn_unpack_associativity() is a const long *, but the > parsing code expects __be64 values actually. This is inconsistent. We should > either pass a const __be64 * or change vphn_unpack_associativity() so that > it fixes endianness by itself. > > This patch does the latter, since the caller doesn't need to know about > endianness and this allows to fix significant 64-bit values only. Please > note that the previous code was able to cope with 32-bit fields being split > accross two consecutives 64-bit values. Since PAPR+ doesn't say this cannot > happen, the behaviour was kept. It requires extra checking to know when fixing > is needed though. While I agree with moving the endian fixing down, the patch makes me nervous. Note that I don't fully understand the format of what we are parsing here so I might be wrong but ... > > #define VPHN_FIELD_UNUSED (0xffff) > #define VPHN_FIELD_MSB (0x8000) > #define VPHN_FIELD_MASK (~VPHN_FIELD_MSB) > > - for (i = 1; i < VPHN_ASSOC_BUFSIZE; i++) { > - if (be16_to_cpup(field) == VPHN_FIELD_UNUSED) > + for (i = 1, j = 0, k = 0; i < VPHN_ASSOC_BUFSIZE;) { > + u16 field; > + > + if (j % 4 == 0) { > + fixed.packed[k] = cpu_to_be64(packed[k]); > + k++; > + } So we have essentially a bunch of 16-bit fields ... the above loads and swap a whole 4 of them at once. However that means not only we byteswap them individually, but we also flip the order of the fields. This is ok ? > + field = be16_to_cpu(fixed.field[j]); > + > + if (field == VPHN_FIELD_UNUSED) > /* All significant fields processed. > */ > break; For example, we might have USED,USED,USED,UNUSED ... after the swap, we now have UNUSED,USED,USED,USED ... and we stop parsing in the above line on the first one. Or am I missing something ? > - if (be16_to_cpup(field) & VPHN_FIELD_MSB) { > + if (field & VPHN_FIELD_MSB) { > /* Data is in the lower 15 bits of this field */ > - unpacked[i] = cpu_to_be32( > - be16_to_cpup(field) & VPHN_FIELD_MASK); > - field++; > + unpacked[i++] = cpu_to_be32(field & VPHN_FIELD_MASK); > + j++; > } else { > /* Data is in the lower 15 bits of this field > * concatenated with the next 16 bit field > */ > - unpacked[i] = *((__be32 *)field); > - field += 2; > + if (unlikely(j % 4 == 3)) { > + /* The next field is to be copied from the next > + * 64-bit input value. We must fix it now. > + */ > + fixed.packed[k] = cpu_to_be64(packed[k]); > + k++; > + } > + > + unpacked[i++] = *((__be32 *)&fixed.field[j]); > + j += 2; > } > } > > @@ -1460,11 +1479,8 @@ static long hcall_vphn(unsigned long cpu, __be32 *associativity) > long retbuf[PLPAR_HCALL9_BUFSIZE] = {0}; > u64 flags = 1; > int hwcpu = get_hard_smp_processor_id(cpu); > - int i; > > rc = plpar_hcall9(H_HOME_NODE_ASSOCIATIVITY, retbuf, flags, hwcpu); > - for (i = 0; i < VPHN_REGISTER_COUNT; i++) > - retbuf[i] = cpu_to_be64(retbuf[i]); > vphn_unpack_associativity(retbuf, associativity); > > return rc;