From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [RFC Part1 PATCH v3 13/17] x86/io: Unroll string I/O when SEV is active Date: Wed, 26 Jul 2017 12:45:17 +0200 Message-ID: References: <20170724190757.11278-1-brijesh.singh@amd.com> <20170724190757.11278-14-brijesh.singh@amd.com> <063D6719AE5E284EB5DD2968C1650D6DD003FB85@AcuExch.aculab.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: Brijesh Singh , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "linux-efi@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "kvm@vger.kernel.org" , Fenghua Yu , Matt Fleming , David Howells , Paul Mackerras , "H . Peter Anvin" , Christoph Lameter , Jonathan Corbet , =?UTF-8?Q?Radim_Krcm=C3=A1r?= , Piotr Luc , Ingo Molnar , Dave Airlie , Borislav Petkov , Tom Lendacky Return-path: In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6DD003FB85@AcuExch.aculab.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Tue, Jul 25, 2017 at 11:51 AM, David Laight wrote: > From: Brijesh Singh >> Sent: 24 July 2017 20:08 >> From: Tom Lendacky >> >> Secure Encrypted Virtualization (SEV) does not support string I/O, so >> unroll the string I/O operation into a loop operating on one element at >> a time. >> >> Signed-off-by: Tom Lendacky >> Signed-off-by: Brijesh Singh >> --- >> arch/x86/include/asm/io.h | 26 ++++++++++++++++++++++---- >> 1 file changed, 22 insertions(+), 4 deletions(-) >> >> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h >> index e080a39..2f3c002 100644 >> --- a/arch/x86/include/asm/io.h >> +++ b/arch/x86/include/asm/io.h >> @@ -327,14 +327,32 @@ static inline unsigned type in##bwl##_p(int port) \ >> \ >> static inline void outs##bwl(int port, const void *addr, unsigned long count) \ >> { This will clash with a fix I did to add a "memory" clobber for the traditional implementation, see https://patchwork.kernel.org/patch/9854573/ > Is it even worth leaving these as inline functions? > Given the speed of IO cycles it is unlikely that the cost of calling a real > function will be significant. > The code bloat reduction will be significant. I think the smallest code would be the original "rep insb" etc, which should be smaller than a function call, unlike the loop. Then again, there is a rather small number of affected device drivers, almost all of them for ancient hardware that you won't even build in a 64-bit x86 kernel, see the list below. The only user I found that is actually still relevant is drivers/tty/hvc/hvc_xen.c, which uses it for the early console. Arnd --- Full list for reference $ git grep -wl '\(__ide_\|\)\(in\|out\)s\(b\|w\|l\)' drivers sound/ drivers/atm/horizon.c drivers/cdrom/gdrom.c drivers/gpu/drm/vmwgfx/vmwgfx_msg.h drivers/ide/ide-io-std.c drivers/isdn/hardware/avm/avmcard.h drivers/isdn/hardware/eicon/divasmain.c drivers/isdn/hardware/mISDN/avmfritz.c drivers/isdn/hardware/mISDN/iohelper.h drivers/isdn/hardware/mISDN/netjet.c drivers/isdn/hardware/mISDN/w6692.c drivers/isdn/hisax/asuscom.c drivers/isdn/hisax/avm_a1.c drivers/isdn/hisax/avm_a1p.c drivers/isdn/hisax/avm_pci.c drivers/isdn/hisax/diva.c drivers/isdn/hisax/elsa.c drivers/isdn/hisax/gazel.c drivers/isdn/hisax/hisax_fcpcipnp.c drivers/isdn/hisax/ix1_micro.c drivers/isdn/hisax/mic.c drivers/isdn/hisax/netjet.c drivers/isdn/hisax/niccy.c drivers/isdn/hisax/saphir.c drivers/isdn/hisax/sedlbauer.c drivers/isdn/hisax/sportster.c drivers/isdn/hisax/teles3.c drivers/isdn/hisax/w6692.c drivers/isdn/hisax/w6692.h drivers/media/rc/winbond-cir.c drivers/mtd/spi-nor/aspeed-smc.c drivers/net/appletalk/cops.c drivers/net/arcnet/arcdevice.h drivers/net/arcnet/com20020.c drivers/net/ethernet/3com/3c509.c drivers/net/ethernet/3com/3c515.c drivers/net/ethernet/3com/3c574_cs.c drivers/net/ethernet/3com/3c589_cs.c drivers/net/ethernet/8390/axnet_cs.c drivers/net/ethernet/8390/mcf8390.c drivers/net/ethernet/8390/ne.c drivers/net/ethernet/8390/ne2k-pci.c drivers/net/ethernet/8390/pcnet_cs.c drivers/net/ethernet/8390/smc-ultra.c drivers/net/ethernet/amd/nmclan_cs.c drivers/net/ethernet/fujitsu/fmvj18x_cs.c drivers/net/ethernet/hp/hp100.c drivers/net/ethernet/smsc/smc9194.c drivers/net/ethernet/smsc/smc91c92_cs.c drivers/net/ethernet/smsc/smc91x.h drivers/net/ethernet/xircom/xirc2ps_cs.c drivers/net/sb1000.c drivers/net/wan/sbni.c drivers/net/wireless/cisco/airo.c drivers/net/wireless/intersil/hostap/hostap_cs.c drivers/net/wireless/intersil/hostap/hostap_plx.c drivers/net/wireless/marvell/libertas/if_cs.c drivers/net/wireless/wl3501_cs.c drivers/parport/parport_pc.c drivers/pcmcia/m32r_cfc.c drivers/scsi/NCR53c406a.c drivers/scsi/aha152x.c drivers/scsi/eata_pio.c drivers/scsi/fdomain.c drivers/scsi/g_NCR5380.c drivers/scsi/imm.c drivers/scsi/nsp32_io.h drivers/scsi/pcmcia/nsp_io.h drivers/scsi/pcmcia/sym53c500_cs.c drivers/scsi/ppa.c drivers/scsi/qlogicfas408.c drivers/scsi/sym53c416.c drivers/staging/comedi/drivers/adl_pci9111.c drivers/staging/comedi/drivers/cb_pcidas.c drivers/staging/comedi/drivers/das16m1.c drivers/staging/comedi/drivers/das1800.c drivers/staging/iio/adc/ad7606_par.c drivers/tty/hvc/hvc_xen.c drivers/tty/isicom.c drivers/tty/rocket_int.h drivers/usb/host/isp1362.h drivers/usb/musb/blackfin.c sound/drivers/opl4/opl4_lib.c sound/isa/gus/gus_dram.c sound/isa/gus/gus_pcm.c