On Wed, Apr 04, 2018 at 02:28:52PM +0100, James Morse wrote: > Hi Kostiantyn, > > On 04/04/18 13:45, Kostiantyn Iarmak wrote: > > From: Pratyush Anand <panand@xxxxxxxxxx> > >> Date: Fri, Jun 2, 2017 at 5:42 PM > >> Subject: Re: [PATCH v3 0/2] kexec-tools: arm64: Enable D-cache in purgatory > >> To: James Morse <james.morse@xxxxxxx> > >> Cc: mark.rutland@xxxxxxx, bhe@xxxxxxxxxx, kexec@xxxxxxxxxxxxxxxxxxx, > >> horms@xxxxxxxxxxxx, dyoung@xxxxxxxxxx, > >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > >> > >> On Friday 02 June 2017 01:53 PM, James Morse wrote: > >>> On 23/05/17 06:02, Pratyush Anand wrote: > >>>> It takes more that 2 minutes to verify SHA in purgatory when vmlinuz image > >>>> is around 13MB and initramfs is around 30MB. It takes more than 20 second > >>>> even when we have -O2 optimization enabled. However, if dcache is enabled > >>>> during purgatory execution then, it takes just a second in SHA > >>>> verification. > >>>> > >>>> Therefore, these patches adds support for dcache enabling facility during > >>>> purgatory execution. > > >>> I'm still not convinced we need this. Moving the SHA verification to happen > >>> before the dcache+mmu are disabled would also solve the delay problem, > >> > >> Humm..I am not sure, if we can do that. > > >> When we leave kernel (and enter into purgatory), icache+dcache+mmu are > >> already disabled. I think, that would be possible when we will be in a > >> position to use in-kernel purgatory. > >> > >>> and we > >>> can print an error message or fail the syscall. > >>> > >>> For kexec we don't expect memory corruption, what are we testing for? > >>> I can see the use for kdump, but the kdump-kernel is unmapped so the kernel > >>> can't accidentally write over it. > >>> > >>> (we discussed all this last time, but it fizzled-out. If you and the > >>> kexec-tools maintainer think its necessary, fine by me!) > > >> Yes, there had already been discussion and MAINTAINERs have > >> discouraged none-purgatory implementation. I don't remember the discussion like this quite well, but anyhow ... > >> > >>> I have some comments on making this code easier to maintain.. > >>> > >> Thanks. > >> > >> I have implemented your review comments and have archived the code in > >> > >> https://github.com/pratyushanand/kexec-tools.git : purgatory-enable-dcache > >> > >> I will be posting the next version only when someone complains about > >> ARM64 kdump behavior that it is not as fast as x86. > > > On our ARM64-based platform we have very long main kernel-secondary kernel > > switch time. > > > > This patch set fixes the issue (we are using 4.4 kernel and 2.0.13 kexec-tools > > version), we can get ~25x speedup, with this patch secondary kernel boots in ~3 > > seconds while on 2.0.13-2.0.16 kexec-tools without this patch switch takes about > > 75 seconds. > > This is slow because its generating a checksum of the kernel without the benefit > of the caches. This series generated page tables so that it could enable the MMU > and caches. But, the purgatory code also needs to be a simple as possible > because its practically impossible to debug. Not impossible, but I admit that I occasionally had hard time in debugging. > The purgatory code does this checksum-ing because its worried the panic() was > because the kernel cause some memory corruption, and that memory corruption may > have affected the kdump kernel too. > > This can't happen on arm64 as we unmap kdump's crash region, so not even the > kernel can accidentally write to it. 98d2e1539b84 ("arm64: kdump: protect crash > dump kernel memory") has all the details. > > (we also needed to do this to avoid the risk of mismatched memory attributes if > kdump boots and some CPUs are still stuck in the old kernel) > > > > When do you plan merge this patch? > > We ended up with the check-summing code because its the default behaviour of > kexec-tools on other architectures. > > One alternative is to rip it out for arm64. Untested: Thanks for the patch. This eventually eliminates "reason d'etre" of purgatory on arm64 as I does in my kexec_file patch, although it would require a small re-work. -Takahiro AKASHI > --------------------%<-------------------- > diff --git a/purgatory/arch/arm64/Makefile b/purgatory/arch/arm64/Makefile > index 636abea..f10c148 100644 > --- a/purgatory/arch/arm64/Makefile > +++ b/purgatory/arch/arm64/Makefile > @@ -7,7 +7,8 @@ arm64_PURGATORY_EXTRA_CFLAGS = \ > -Werror-implicit-function-declaration \ > -Wdeclaration-after-statement \ > -Werror=implicit-int \ > - -Werror=strict-prototypes > + -Werror=strict-prototypes \ > + -DNO_SHA_IN_PURGATORY > > arm64_PURGATORY_SRCS += \ > purgatory/arch/arm64/entry.S \ > diff --git a/purgatory/purgatory.c b/purgatory/purgatory.c > index 3bbcc09..44e792a 100644 > --- a/purgatory/purgatory.c > +++ b/purgatory/purgatory.c > @@ -9,6 +9,8 @@ > struct sha256_region sha256_regions[SHA256_REGIONS] = {}; > sha256_digest_t sha256_digest = { }; > > +#ifndef NO_SHA_IN_PURGATORY > + > int verify_sha256_digest(void) > { > struct sha256_region *ptr, *end; > @@ -39,14 +41,18 @@ int verify_sha256_digest(void) > return 0; > } > > +#endif /* NO_SHA_IN_PURGATORY */ > + > void purgatory(void) > { > printf("I'm in purgatory\n"); > setup_arch(); > +#ifndef NO_SHA_IN_PURGATORY > if (verify_sha256_digest()) { > for(;;) { > /* loop forever */ > } > } > +#endif /* NO_SHA_IN_PURGATORY */ > post_verification_setup_arch(); > } > --------------------%<-------------------- > > > Thanks, > > James > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
