Buildresult: linus/acs5k_tiny_defconfig/arm-gcc4.6 built on Feb 2 2019, 07:56

kisskb

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Status:	OK
Date/Time:	Feb 2 2019, 07:56
Duration:	0:00:24.335219
Builder:	ka1
Revision:	x86: explicitly align IO accesses in memcpy_{to,from}io (`c228d294f2040c3a5f5965ff04d4947d0bf6e7da)`
Target:	linus/acs5k_tiny_defconfig/arm-gcc4.6
Branch:	linus
Compiler:	arm-gcc4.6 (arm-unknown-linux-gnueabi-gcc (GCC) 4.6.3 / GNU ld (GNU Binutils) 2.22)
Config:	acs5k_tiny_defconfig (download)
Log:	Download original Possible warnings (6) kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized] drivers/base/regmap/regmap.c:2594:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] drivers/base/regmap/regmap.c:1855:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized] drivers/i2c/i2c-core-base.c:235:5: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] include/linux/skbuff.h:1338:6: warning: 'extra_uref' may be used uninitialized in this function [-Wuninitialized] Full Log # git rev-parse -q --verify c228d294f2040c3a5f5965ff04d4947d0bf6e7da^{commit} c228d294f2040c3a5f5965ff04d4947d0bf6e7da already have revision, skipping fetch # git checkout -q -f -B kisskb c228d294f2040c3a5f5965ff04d4947d0bf6e7da # git clean -qxdf # < git log -1 # commit c228d294f2040c3a5f5965ff04d4947d0bf6e7da # Author: Linus Torvalds <torvalds@linux-foundation.org> # Date: Thu Jan 31 11:10:20 2019 -0800 # # x86: explicitly align IO accesses in memcpy_{to,from}io # # In commit 170d13ca3a2f ("x86: re-introduce non-generic memcpy_{to,from}io") # I made our copy from IO space use a separate copy routine rather than # rely on the generic memcpy. I did that because our generic memory copy # isn't actually well-defined when it comes to internal access ordering or # alignment, and will in fact depend on various CPUID flags. # # In particular, the default memcpy() for a modern Intel CPU will # generally be just a "rep movsb", which works reasonably well for # medium-sized memory copies of regular RAM, since the CPU will turn it # into fairly optimized microcode. # # However, for non-cached memory and IO, "rep movs" ends up being # horrendously slow and will just do the architectural "one byte at a # time" accesses implied by the movsb. # # At the other end of the spectrum, if you _don't_ end up using the "rep # movsb" code, you'd likely fall back to the software copy, which does # overlapping accesses for the tail, and may copy things backwards. # Again, for regular memory that's fine, for IO memory not so much. # # The thinking was that clearly nobody really cared (because things # worked), but some people had seen horrible performance due to the byte # accesses, so let's just revert back to our long ago version that dod # "rep movsl" for the bulk of the copy, and then fixed up the potentially # last few bytes of the tail with "movsw/b". # # Interestingly (and perhaps not entirely surprisingly), while that was # our original memory copy implementation, and had been used before for # IO, in the meantime many new users of memcpy_io() had come about. And # while the access patterns for the memory copy weren't well-defined (so # arguably _any_ access pattern should work), in practice the "rep movsb" # case had been very common for the last several years. # # In particular Jarkko Sakkinen reported that the memcpy_io() change # resuled in weird errors from his Geminilake NUC TPM module. # # And it turns out that the TPM TCG accesses according to spec require # that the accesses be # # (a) done strictly sequentially # # (b) be naturally aligned # # otherwise the TPM chip will abort the PCI transaction. # # And, in fact, the tpm_crb.c driver did this: # # memcpy_fromio(buf, priv->rsp, 6); # ... # memcpy_fromio(&buf[6], &priv->rsp[6], expected - 6); # # which really should never have worked in the first place, but back # before commit 170d13ca3a2f it happened to work, because the # memcpy_fromio() would be expanded to a regular memcpy, and # # (a) gcc would expand the first memcpy in-line, and turn it into a # 4-byte and a 2-byte read, and they happened to be in the right # order, and the alignment was right. # # (b) gcc would call "memcpy()" for the second one, and the machines that # had this TPM chip also apparently ended up always having ERMS # ("Enhanced REP MOVSB/STOSB instructions"), so we'd use the "rep # movbs" for that copy. # # In other words, basically by pure luck, the code happened to use the # right access sizes in the (two different!) memcpy() implementations to # make it all work. # # But after commit 170d13ca3a2f, both of the memcpy_fromio() calls # resulted in a call to the routine with the consistent memory accesses, # and in both cases it started out transferring with 4-byte accesses. # Which worked for the first copy, but resulted in the second copy doing a # 32-bit read at an address that was only 2-byte aligned. # # Jarkko is actually fixing the fragile code in the TPM driver, but since # this is an excellent example of why we absolutely must not use a generic # memcpy for IO accesses, _and_ an IO-specific one really should strive to # align the IO accesses, let's do exactly that. # # Side note: Jarkko also noted that the driver had been used on ARM # platforms, and had worked. That was because on 32-bit ARM, memcpy_io() # ends up always doing byte accesses, and on 64-bit ARM it first does byte # accesses to align to 8-byte boundaries, and then does 8-byte accesses # for the bulk. # # So ARM actually worked by design, and the x86 case worked by pure luck. # # We might* want to make x86-64 do the 8-byte case too. That should be a # pretty straightforward extension, but let's do one thing at a time. And # generally MMIO accesses aren't really all that performance-critical, as # shown by the fact that for a long time we just did them a byte at a # time, and very few people ever noticed. # # Reported-and-tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> # Tested-by: Jerry Snitselaar <jsnitsel@redhat.com> # Cc: David Laight <David.Laight@aculab.com> # Fixes: 170d13ca3a2f ("x86: re-introduce non-generic memcpy_{to,from}io") # Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> # < /opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc --version # < /opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-ld --version # < git log --format=%s --max-count=1 c228d294f2040c3a5f5965ff04d4947d0bf6e7da # < make -s -j 48 ARCH=arm O=/kisskb/build/linus_acs5k_tiny_defconfig_arm CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi- acs5k_tiny_defconfig # make -s -j 48 ARCH=arm O=/kisskb/build/linus_acs5k_tiny_defconfig_arm CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi- /kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl': /kisskb/src/kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/base/regmap/regmap.c: In function 'regmap_raw_read': /kisskb/src/drivers/base/regmap/regmap.c:2594:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/drivers/base/regmap/regmap.c: In function '_regmap_raw_write': /kisskb/src/drivers/base/regmap/regmap.c:1855:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c: In function 'proc_reg_open': /kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/fs/proc/inode.c:339:21: note: 'pdeo' was declared here /kisskb/src/drivers/i2c/i2c-core-base.c: In function 'i2c_generic_scl_recovery': /kisskb/src/drivers/i2c/i2c-core-base.c:235:5: warning: 'ret' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/net/ipv4/ip_output.c: In function '__ip_append_data': /kisskb/src/include/linux/skbuff.h:1338:6: warning: 'extra_uref' may be used uninitialized in this function [-Wuninitialized] /kisskb/src/net/ipv4/ip_output.c:885:14: note: 'extra_uref' was declared here Completed OK # rm -rf /kisskb/build/linus_acs5k_tiny_defconfig_arm # Build took: 0:00:24.335219

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