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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: xen-devel@lists.xenproject.org,
	Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
	paul@xen.org
Subject: Re: [PATCH for-4.14 2/8] x86/hvm: don't force vCPU 0 for IRQ 0 when using fixed destination mode
Date: Thu, 18 Jun 2020 16:18:05 +0200	[thread overview]
Message-ID: <20200618141805.GR735@Air-de-Roger> (raw)
In-Reply-To: <ddaeb562-1d61-1855-508c-40bb2b796357@suse.com>

On Thu, Jun 18, 2020 at 04:08:28PM +0200, Jan Beulich wrote:
> On 18.06.2020 15:48, Roger Pau Monné wrote:
> > On Thu, Jun 18, 2020 at 03:43:00PM +0200, Jan Beulich wrote:
> >> On 12.06.2020 17:56, Roger Pau Monne wrote:
> >>> When the IO APIC pin mapped to the ISA IRQ 0 has been configured to
> >>> use fixed delivery mode do not forcefully route interrupts to vCPU 0,
> >>> as the OS might have setup those interrupts to be injected to a
> >>> different vCPU, and injecting to vCPU 0 can cause the OS to miss such
> >>> interrupts or errors to happen due to unexpected vectors being
> >>> injected on vCPU 0.
> >>>
> >>> In order to fix remove such handling altogether for fixed destination
> >>> mode pins and just inject them according to the data setup in the
> >>> IO-APIC entry.
> >>>
> >>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> >>
> >> Technically
> >> Reviewed-by: Jan Beulich <jbeulich@suse.com>
> >>
> >> I wonder though why this was done in the first place - it very much
> >> feels like a workaround for certain guest behavior, and hence
> >> getting rid of it may mean a certain risk of regressions. Not a
> >> very good point in time to make risky changes ...
> > 
> > We can defer to after the release I guess, but I will still ask for
> > the changes to be backported.
> 
> That's fine, albeit if we decide to delay it until 4.15 was branched,
> then I think we want to also wait longer than usual until it would hit
> the stable trees. Unfortunately c8e79412c001's description is of no
> help to understand what or why "time jumps" may result from delivering
> the interrupt as requested.

Yes, I've also looked at the original commit and have no idea what it
was actually trying to fix, and why delivering to vCPU 0 fixed it.
FWIW, I tried delivering to a different vCPU and it seems to work
fine.

Note that other timers (ie: RTC or HPET) are not tied to vCPU 0, so it
must have been something related to the PIT?

Thanks, Roger.


  reply	other threads:[~2020-06-18 14:18 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12 15:56 [PATCH for-4.14 0/8] x86/vpt: fixes for vpt and enable vPIT for PVH dom0 Roger Pau Monne
2020-06-12 15:56 ` [PATCH for-4.14 1/8] x86/hvm: fix vIO-APIC build without IRQ0_SPECIAL_ROUTING Roger Pau Monne
2020-06-15 10:00   ` Paul Durrant
2020-06-15 11:44     ` Roger Pau Monné
2020-06-12 15:56 ` [PATCH for-4.14 2/8] x86/hvm: don't force vCPU 0 for IRQ 0 when using fixed destination mode Roger Pau Monne
2020-06-18 13:43   ` Jan Beulich
2020-06-18 13:48     ` Roger Pau Monné
2020-06-18 14:08       ` Jan Beulich
2020-06-18 14:18         ` Roger Pau Monné [this message]
2020-06-18 14:29           ` Jan Beulich
2020-06-18 14:49             ` Roger Pau Monné
2020-06-18 15:16               ` Jan Beulich
2020-06-12 15:56 ` [PATCH for-4.14 3/8] x86/hvm: fix ISA IRQ 0 handling when set as lowest priority mode in IO APIC Roger Pau Monne
2020-06-18 14:26   ` Jan Beulich
2020-06-18 14:55     ` Roger Pau Monné
2020-06-18 15:20       ` Jan Beulich
2020-06-12 15:56 ` [PATCH for-4.14 4/8] x86/vpt: only try to resume timers belonging to enabled devices Roger Pau Monne
2020-06-18 14:37   ` Jan Beulich
2020-06-18 14:56     ` Roger Pau Monné
2020-06-12 15:56 ` [PATCH for-4.14 5/8] x86/hvm: only translate ISA interrupts to GSIs in virtual timers Roger Pau Monne
2020-06-18 14:47   ` Jan Beulich
2020-06-18 15:03     ` Roger Pau Monné
2020-06-12 15:56 ` [PATCH for-4.14 6/8] x86/vpt: fix injection to remote vCPU Roger Pau Monne
2020-06-18 15:12   ` Jan Beulich
2020-06-18 17:14     ` Roger Pau Monné
2020-06-19 12:37       ` Jan Beulich
2020-06-12 15:56 ` [PATCH for-4.14 7/8] x86/hvm: add hardware domain support to hvm_isa_irq_to_gsi Roger Pau Monne
2020-06-18 15:37   ` Jan Beulich
2020-06-12 15:56 ` [PATCH for-4.14 8/8] x86/hvm: enable emulated PIT for PVH dom0 Roger Pau Monne
2020-06-15 15:33   ` Andrew Cooper
2020-06-15 15:47     ` Roger Pau Monné
2020-06-18 16:05   ` Jan Beulich
2020-06-29 14:46     ` Roger Pau Monné

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