From: Daniel Axtens <dja@axtens•net>
To: Nicholas Piggin <npiggin@gmail•com>, kvm-ppc@vger•kernel.org
Cc: linuxppc-dev@lists•ozlabs.org,
Nicholas Piggin <npiggin@gmail•com>,
Fabiano Rosas <farosas@linux•ibm.com>
Subject: Re: [PATCH v2 07/37] KVM: PPC: Book3S 64: Move GUEST_MODE_SKIP test into KVM
Date: Fri, 05 Mar 2021 16:54:08 +1100 [thread overview]
Message-ID: <87o8fy87sv.fsf@linkitivity.dja.id.au> (raw)
In-Reply-To: <20210225134652.2127648-8-npiggin@gmail.com>
Hi Nick,
> - .if IKVM_SKIP
> -89: mtocrf 0x80,r9
> - ld r10,IAREA+EX_CTR(r13)
> - mtctr r10
> - ld r9,IAREA+EX_R9(r13)
> - ld r10,IAREA+EX_R10(r13)
> - ld r11,IAREA+EX_R11(r13)
> - ld r12,IAREA+EX_R12(r13)
> - .if IHSRR_IF_HVMODE
> - BEGIN_FTR_SECTION
> - b kvmppc_skip_Hinterrupt
> - FTR_SECTION_ELSE
> - b kvmppc_skip_interrupt
> - ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
I was initially concerned that you were pulling out the complexities
around IHSRR_IF_HVMODE, but I checked exceptions-64s.S and the only
exception handler that sets IHSRR_IF_HVMODE is hardware_interrupt and
that does not set IKVM_SKIP, so we are indeed fine to not keep this
complex little asm section.
> - .elseif IHSRR
> - b kvmppc_skip_Hinterrupt
> - .else
> - b kvmppc_skip_interrupt
> - .endif
> - .endif
> .endm
> +/*
> + * KVM uses a trick where it is running in MSR[HV]=1 mode in real-mode with the
> + * guest MMU context loaded, and it sets KVM_GUEST_MODE_SKIP and enables
> + * MSR[DR]=1 while leaving MSR[IR]=0, so it continues to fetch HV instructions
> + * but loads and stores will access the guest context. This is used to load
> + * the faulting instruction without walking page tables.
> + *
> + * However the guest context may not be able to translate, or it may cause a
> + * machine check or other issue, which will result in a fault in the host
> + * (even with KVM-HV).
> + *
> + * These faults are caught here and if the fault was (or was likely) due to
> + * that load, then we just return with the PC advanced +4 and skip the load,
> + * which then goes via the slow path.
> + */
This is a really helpful comment! Thanks!
> +.Lmaybe_skip:
> + cmpwi r12,BOOK3S_INTERRUPT_MACHINE_CHECK
> + beq 1f
> + cmpwi r12,BOOK3S_INTERRUPT_DATA_STORAGE
> + beq 1f
> + cmpwi r12,BOOK3S_INTERRUPT_DATA_SEGMENT
> + beq 1f
> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> + /* HSRR interrupts have 2 added to trap vector */
> + cmpwi r12,BOOK3S_INTERRUPT_H_DATA_STORAGE | 0x2
This took me by surprise for a while, but I checked how it works in
exceptions-64s.S and indeed the GEN_KVM macro will add 0x2 to the IVEC
if IHSRR is set, and it is set for h_data_storage.
So this checks out to me.
I have checked, to the best of my limited assembler capabilities that
the logic before and after matches. It seems good to me.
On that limited basis,
Reviewed-by: Daniel Axtens <dja@axtens•net>
Kind regards,
Daniel
> + beq 2f
> +#endif
> + b .Lno_skip
> +1: mfspr r9,SPRN_SRR0
> + addi r9,r9,4
> + mtspr SPRN_SRR0,r9
> + ld r12,HSTATE_SCRATCH0(r13)
> + ld r9,HSTATE_SCRATCH2(r13)
> + GET_SCRATCH0(r13)
> + RFI_TO_KERNEL
> +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> +2: mfspr r9,SPRN_HSRR0
> + addi r9,r9,4
> + mtspr SPRN_HSRR0,r9
> + ld r12,HSTATE_SCRATCH0(r13)
> + ld r9,HSTATE_SCRATCH2(r13)
> + GET_SCRATCH0(r13)
> + HRFI_TO_KERNEL
> +#endif
> --
> 2.23.0
next prev parent reply other threads:[~2021-03-05 5:54 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 13:46 [PATCH v2 00/37] KVM: PPC: Book3S: C-ify the P9 entry/exit code Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 01/37] KVM: PPC: Book3S 64: remove unused kvmppc_h_protect argument Nicholas Piggin
2021-02-26 5:01 ` Daniel Axtens
2021-02-26 23:50 ` Nicholas Piggin
2021-03-05 4:45 ` Daniel Axtens
2021-02-25 13:46 ` [PATCH v2 02/37] KVM: PPC: Book3S HV: Fix CONFIG_SPAPR_TCE_IOMMU=n default hcalls Nicholas Piggin
2021-02-26 5:21 ` Daniel Axtens
2021-02-25 13:46 ` [PATCH v2 03/37] powerpc/64s: Remove KVM handler support from CBE_RAS interrupts Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 04/37] powerpc/64s: remove KVM SKIP test from instruction breakpoint handler Nicholas Piggin
2021-02-26 5:44 ` Daniel Axtens
2021-02-26 23:51 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 05/37] KVM: PPC: Book3S HV: Ensure MSR[ME] is always set in guest MSR Nicholas Piggin
2021-02-26 6:06 ` Daniel Axtens
2021-02-26 23:55 ` Nicholas Piggin
2021-03-05 4:50 ` Daniel Axtens
2021-02-25 13:46 ` [PATCH v2 06/37] KVM: PPC: Book3S 64: move KVM interrupt entry to a common entry point Nicholas Piggin
2021-03-05 5:03 ` Daniel Axtens
2021-02-25 13:46 ` [PATCH v2 07/37] KVM: PPC: Book3S 64: Move GUEST_MODE_SKIP test into KVM Nicholas Piggin
2021-03-05 5:54 ` Daniel Axtens [this message]
2021-02-25 13:46 ` [PATCH v2 08/37] KVM: PPC: Book3S 64: add hcall interrupt handler Nicholas Piggin
2021-03-05 6:03 ` Daniel Axtens
2021-02-25 13:46 ` [PATCH v2 09/37] KVM: PPC: Book3S 64: Move hcall early register setup to KVM Nicholas Piggin
2021-03-05 6:48 ` Daniel Axtens
2021-02-25 13:46 ` [PATCH v2 10/37] KVM: PPC: Book3S 64: Move interrupt " Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 11/37] KVM: PPC: Book3S 64: move bad_host_intr check to HV handler Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 12/37] KVM: PPC: Book3S 64: Minimise hcall handler calling convention differences Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 13/37] KVM: PPC: Book3S HV P9: Move radix MMU switching instructions together Nicholas Piggin
2021-02-26 15:56 ` Fabiano Rosas
2021-02-26 23:57 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 14/37] KVM: PPC: Book3S HV P9: implement kvmppc_xive_pull_vcpu in C Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 15/37] KVM: PPC: Book3S HV P9: Move xive vcpu context management into kvmhv_p9_guest_entry Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 16/37] KVM: PPC: Book3S HV P9: Stop handling hcalls in real-mode in the P9 path Nicholas Piggin
2021-02-25 14:51 ` Cédric Le Goater
2021-02-26 23:59 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 17/37] KVM: PPC: Book3S HV P9: Move setting HDEC after switching to guest LPCR Nicholas Piggin
2021-02-26 16:38 ` Fabiano Rosas
2021-02-26 23:59 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 18/37] KVM: PPC: Book3S HV P9: Use large decrementer for HDEC Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 19/37] KVM: PPC: Book3S HV P9: Use host timer accounting to avoid decrementer read Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 20/37] KVM: PPC: Book3S HV P9: Reduce mftb per guest entry/exit Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 21/37] powerpc: add set_dec_or_work API for safely updating decrementer Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 22/37] KVM: PPC: Book3S HV P9: Reduce irq_work vs guest decrementer races Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 23/37] KVM: PPC: Book3S HV P9: Implement the rest of the P9 path in C Nicholas Piggin
2021-02-26 22:37 ` Fabiano Rosas
2021-02-27 0:21 ` Nicholas Piggin
2021-02-27 0:55 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 24/37] KVM: PPC: Book3S HV P9: inline kvmhv_load_hv_regs_and_go into __kvmhv_vcpu_entry_p9 Nicholas Piggin
2021-03-02 13:48 ` Fabiano Rosas
2021-02-25 13:46 ` [PATCH v2 25/37] KVM: PPC: Book3S HV P9: Read machine check registers while MSR[RI] is 0 Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 26/37] KVM: PPC: Book3S HV P9: Improve exit timing accounting coverage Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 27/37] KVM: PPC: Book3S HV P9: Move SPR loading after expiry time check Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 28/37] KVM: PPC: Book3S HV P9: Add helpers for OS SPR handling Nicholas Piggin
2021-03-02 15:04 ` Fabiano Rosas
2021-03-04 11:02 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 29/37] KVM: PPC: Book3S HV P9: Switch to guest MMU context as late as possible Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 30/37] KVM: PPC: Book3S HV: Implement radix prefetch workaround by disabling MMU Nicholas Piggin
2021-03-02 21:21 ` Fabiano Rosas
2021-03-04 11:04 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 31/37] KVM: PPC: Book3S HV: Remove support for dependent threads mode on P9 Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 32/37] KVM: PPC: Book3S HV: Remove radix guest support from P7/8 path Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 33/37] KVM: PPC: Book3S HV: small pseries_do_hcall cleanup Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 34/37] KVM: PPC: Book3S HV: add virtual mode handlers for HPT hcalls and page faults Nicholas Piggin
2021-03-03 20:09 ` Fabiano Rosas
2021-03-04 11:05 ` Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 35/37] KVM: PPC: Book3S HV P9: implement hash guest support Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 36/37] KVM: PPC: Book3S HV P9: implement hash host / " Nicholas Piggin
2021-02-25 13:46 ` [PATCH v2 37/37] KVM: PPC: Book3S HV: remove POWER9 support from P7/8 paths Nicholas Piggin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87o8fy87sv.fsf@linkitivity.dja.id.au \
--to=dja@axtens$(echo .)net \
--cc=farosas@linux$(echo .)ibm.com \
--cc=kvm-ppc@vger$(echo .)kernel.org \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=npiggin@gmail$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox