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

Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx> · Fri, 24 Nov 2023 18:04:41 +0530

On 24-11-2023 03:49 pm, Marc Zyngier wrote:
On Fri, 24 Nov 2023 09:50:33 +0000,
Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx> wrote:

On 23-11-2023 10:14 pm, Marc Zyngier wrote:
On Thu, 23 Nov 2023 16:21:48 +0000,
Miguel Luis <miguel.luis@xxxxxxxxxx> 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@xxxxxxxxxx> wrote:
Hi Marc,

On 20 Nov 2023, at 12:09, Marc Zyngier <maz@xxxxxxxxxx> 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@xxxxxxxxxx
[2] https://lore.kernel.org/r/20231120123721.851738-1-maz@xxxxxxxxxx
[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)?

I have dumped HCR_EL2 before entry to L1 in both V11 and V10.
on V10 HCR_EL2=0x2743c827c263f
on V11 HCR_EL2=0x27c3c827c263f

on V11 the function vcpu_el2_e2h_is_set(vcpu) is returning false
resulting in NV1 bit set along with NV and NV2.
AFAIK, For L1 to be in VHE, NV1 bit should be zero and NV=NV2=1.

I could boot L1 then L2, if I hack vcpu_el2_e2h_is_set to return true.
There could be a bug in V11 or E2H0 patchset resulting in
vcpu_el2_e2h_is_set() returning false?

The E2H0 series should only force vcpu_el2_e2h_is_set() to return
true, but not set it to false. Can you dump the *guest's* version of
HCR_EL2 at this point?

with V11: vhcr_el2=0x100030080000000 mask=0x100af00ffffffff
with V10: vhcr_el2=0x488000000
with hack+V11: vhcr_el2=0x488000000 mask=0x100af00ffffffff

Thanks,
Ganapat