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[Xen-devel] Rats nest with domain pirq initialisation


  • To: Xen-devel <xen-devel@xxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 4 Sep 2018 19:44:30 +0100
  • Autocrypt: addr=andrew.cooper3@xxxxxxxxxx; prefer-encrypt=mutual; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA==
  • Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Tue, 04 Sep 2018 18:44:56 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 13/08/18 11:01, Andrew Cooper wrote:
> This is in preparation to set up d->max_cpus and d->vcpu[] in domain_create(),
> and allow later parts of domain construction to have access to the values.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  xen/common/domain.c | 34 +++++++++++++++++-----------------
>  1 file changed, 17 insertions(+), 17 deletions(-)
>
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index be51426..0c44f27 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -322,6 +322,23 @@ struct domain *domain_create(domid_t domid,
>          else
>              d->guest_type = guest_type_pv;
>  
> +        if ( !is_hardware_domain(d) )
> +            d->nr_pirqs = nr_static_irqs + extra_domU_irqs;
> +        else
> +            d->nr_pirqs = extra_hwdom_irqs ? nr_static_irqs + 
> extra_hwdom_irqs
> +                                           : arch_hwdom_irqs(domid);
> +        if ( d->nr_pirqs > nr_irqs )
> +            d->nr_pirqs = nr_irqs;
> +
> +        radix_tree_init(&d->pirq_tree);
> +    }
> +
> +    if ( (err = arch_domain_create(d, config)) != 0 )
> +        goto fail;
> +    init_status |= INIT_arch;
> +
> +    if ( !is_idle_domain(d) )
> +    {
>          watchdog_domain_init(d);
>          init_status |= INIT_watchdog;
>  
> @@ -352,16 +369,6 @@ struct domain *domain_create(domid_t domid,

Between these two hunks is:

        d->iomem_caps = rangeset_new(d, "I/O Memory",
RANGESETF_prettyprint_hex);
        d->irq_caps   = rangeset_new(d, "Interrupts", 0);

which is important, because it turns out that x86's
arch_domain_destroy() depends on d->irq_caps already being initialised.

The path which blows up is:

arch_domain_destroy()
  free_domain_pirqs()
    unmap_domain_pirq()
      irq_deny_access()
        rangeset_remove_singleton((d)->irq_caps, i)

Unlike the boolean-nature rangeset_contains_*() helpers, I don't think
it is reasonable to make rangeset_remove_*() tolerate a NULL rangeset.

The behaviour of automatically revoking irq access is dubious at best. 
It is asymmetric with the XEN_DOMCTL_irq_permission, and a caller would
reasonably expect not to have to re-grant identical permissions as the
irq is mapped/unmapped.  Does anyone know why we have this suspect
behaviour in the first place?

One way or another, this path needs to become idempotent, but simply
throwing some NULL pointer checks into unmap_domain_pirq() doesn't feel
like the right thing to do.


A separate mess is that we appear to allocate full pirq structures for
all legacy irqs for every single domain, in init_domain_irq_mapping(). 
At the very least, this is wasteful as very few domains get access to
real hardware in the first place.

The other thing I notice is that alloc_pirq_struct() is downright
dangerous, as it deliberately tries to allocate half a struct pirq for
the !hvm case.  I can only assume this is a space saving measure, but
there is absolutely no help in the commit message which introduced it
(c/s c24536b636f).

~Andrew

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