[PATCH v11 00/43] KVM: arm64: Nested Virtualization support (FEAT_NV2 only)

Thu Nov 23 08:44:34 PST 2023

On Thu, 23 Nov 2023 16:21:48 +0000,
Miguel Luis <miguel.luis at oracle.com> wrote:
> 
> Hi Marc,
> 
> On 21/11/2023 18:02, Marc Zyngier wrote:
> > On Tue, 21 Nov 2023 16:49:52 +0000,
> > Miguel Luis <miguel.luis at oracle.com> wrote:
> >> Hi Marc,
> >>
> >>> On 20 Nov 2023, at 12:09, Marc Zyngier <maz at kernel.org> wrote:
> >>>
> >>> This is the 5th drop of NV support on arm64 for this year, and most
> >>> probably the last one for this side of Christmas.
> >>>
> >>> For the previous episodes, see [1].
> >>>
> >>> What's changed:
> >>>
> >>> - Drop support for the original FEAT_NV. No existing hardware supports
> >>>  it without FEAT_NV2, and the architecture is deprecating the former
> >>>  entirely. This results in fewer patches, and a slightly simpler
> >>>  model overall.
> >>>
> >>> - Reorganise the series to make it a bit more logical now that FEAT_NV
> >>>  is gone.
> >>>
> >>> - Apply the NV idreg restrictions on VM first run rather than on each
> >>>  access.
> >>>
> >>> - Make the nested vgic shadow CPU interface a per-CPU structure rather
> >>>  than per-vcpu.
> >>>
> >>> - Fix the EL0 timer fastpath
> >>>
> >>> - Work around the architecture deficiencies when trapping WFI from a
> >>>  L2 guest.
> >>>
> >>> - Fix sampling of nested vgic state (MISR, ELRSR, EISR)
> >>>
> >>> - Drop the patches that have already been merged (NV trap forwarding,
> >>>  per-MMU VTCR)
> >>>
> >>> - Rebased on top of 6.7-rc2 + the FEAT_E2H0 support [2].
> >>>
> >>> The branch containing these patches (and more) is at [3]. As for the
> >>> previous rounds, my intention is to take a prefix of this series into
> >>> 6.8, provided that it gets enough reviewing.
> >>>
> >>> [1] https://lore.kernel.org/r/20230515173103.1017669-1-maz@kernel.org
> >>> [2] https://lore.kernel.org/r/20231120123721.851738-1-maz@kernel.org
> >>> [3] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/nv-6.8-nv2-only
> >>>
> >> While I was testing this with kvmtool for 5.16 I noted the following on dmesg:
> >>
> >> [  803.014258] kvm [19040]: Unsupported guest sys_reg access at: 8129fa50 [600003c9]
> >>                 { Op0( 3), Op1( 5), CRn( 1), CRm( 0), Op2( 2), func_read },
> >>
> >> This is CPACR_EL12.
> > CPACR_EL12 is redirected to VNCR[0x100]. It really shouldn't trap...
> >
> >> Still need yet to debug.
> > Can you disassemble the guest around the offending PC?
> 
> [ 1248.686350] kvm [7013]: Unsupported guest sys_reg access at: 812baa50 [600003c9]
>                 { Op0( 3), Op1( 5), CRn( 1), CRm( 0), Op2( 2), func_read },
> 
>  12baa00:    14000008     b    0x12baa20
>  12baa04:    d000d501     adrp    x1, 0x2d5c000
>  12baa08:    91154021     add    x1, x1, #0x550
>  12baa0c:    f9400022     ldr    x2, [x1]
>  12baa10:    f9400421     ldr    x1, [x1, #8]
>  12baa14:    8a010042     and    x2, x2, x1
>  12baa18:    d3441c42     ubfx    x2, x2, #4, #4
>  12baa1c:    b4000082     cbz    x2, 0x12baa2c
>  12baa20:    d2a175a0     mov    x0, #0xbad0000                 // #195887104
>  12baa24:    f2994220     movk    x0, #0xca11
>  12baa28:    d69f03e0     eret
>  12baa2c:    d2c00080     mov    x0, #0x400000000               // #17179869184
>  12baa30:    f2b10000     movk    x0, #0x8800, lsl #16
>  12baa34:    f2800000     movk    x0, #0x0
>  12baa38:    d51c1100     msr    hcr_el2, x0
>  12baa3c:    d5033fdf     isb
>  12baa40:    d53c4100     mrs    x0, sp_el1
>  12baa44:    9100001f     mov    sp, x0
>  12baa48:    d538d080     mrs    x0, tpidr_el1
>  12baa4c:    d51cd040     msr    tpidr_el2, x0
>  12baa50:    d53d1040     mrs    x0, cpacr_el12
>  12baa54:    d5181040     msr    cpacr_el1, x0
>  12baa58:    d53dc000     mrs    x0, vbar_el12
>  12baa5c:    d518c000     msr    vbar_el1, x0
>  12baa60:    d53c1120     mrs    x0, mdcr_el2
>  12baa64:    9272f400     and    x0, x0, #0xffffffffffffcfff
>  12baa68:    9266f400     and    x0, x0, #0xfffffffffcffffff
>  12baa6c:    d51c1120     msr    mdcr_el2, x0
>  12baa70:    d53d2040     mrs    x0, tcr_el12
>  12baa74:    d5182040     msr    tcr_el1, x0
>  12baa78:    d53d2000     mrs    x0, ttbr0_el12
>  12baa7c:    d5182000     msr    ttbr0_el1, x0
>  12baa80:    d53d2020     mrs    x0, ttbr1_el12
>  12baa84:    d5182020     msr    ttbr1_el1, x0
>  12baa88:    d53da200     mrs    x0, mair_el12
>  12baa8c:    d518a200     msr    mair_el1, x0
>  12baa90:    d5380761     mrs    x1, s3_0_c0_c7_3
>  12baa94:    d3400c21     ubfx    x1, x1, #0, #4
>  12baa98:    b4000141     cbz    x1, 0x12baac0
>  12baa9c:    d53d2060     mrs    x0, s3_5_c2_c0_3

OK, this is suspiciously close to the location Ganapatrao was having
issues with. Are you running on the same hardware?

In any case, we should never take a trap for this access. Can you dump
HCR_EL2 at the point where the guest traps (in switch.c)?

> >> As for QEMU, it is having issues enabling _EL2 feature although EL2
> >> is supported by checking KVM_CAP_ARM_EL2; need yet to debug this.
> > The capability number changes at each release. Make sure you resync
> > your includes.
> 
> Been there but it seems a different problem this time.

Creating the VM with SVE? NV doesn't support it yet (and it has been
the case for a long while).

	M.

-- 
Without deviation from the norm, progress is not possible.