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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: epam.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: GV1PR03MB10456.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 23a5be2c-271c-49dd-36ee-08de02838e50 X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Oct 2025 13:48:38.4596 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b41b72d0-4e9f-4c26-8a69-f949f367c91d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: 9LeWGVPAcTiSg4AFpN8b/mCPvwpHdp+qocQ7FOLihIwSLL02CJxdku4hpzVYc+7h1Aa3ZB5ArARRoAazhQms2O1lrD11Rl0vjWW5JqSjGcs= X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM4PR03MB11056 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251003_064853_964078_BFBF7738 X-CRM114-Status: GOOD ( 20.14 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Oliver, Oliver Upton writes: > Hi Volodymyr, > > On Thu, Oct 02, 2025 at 09:00:11PM +0000, Volodymyr Babchuk wrote: >> Difference between nested virtualization and "baremetal" case is that >> real GIC can track lots of active interrupts simultaneously, but vGIC >> is limited only to 4..16 LRs. > > There isn't an architectural limitation here. Nothing prevents a > virtualized GIC from representing more active IRQs than there are LRs in > hardware. > > ICH_HCR_EL2.LRENPIE allows you to take a trap when an EOI is received > for an IRQ that exists outside of teh list registers which would allow > the deactivation of the SW view of that IRQ. Ah, right. I am missed this feature. > > As Marc suggested, the correct thing to do is adjust the sorting of IRQs > such that pending IRQs fill LRs before those in an active state. Looks like I missed an email where he suggested that, but yeah, this was my first ideal as well, I just didn't knew about LRENPIE bit. [...] > I'd really like to see a solution similar to Marc's proposal which > addresses the fundamental problem of active IRQs overflowing the list > registers. > I'm sorry but it appears that I won't be able to put any more effort into this issue right now. My boss wants me to switch to another pressing task... So yeah, I won't mind if someone else will continue the work. Also, I am sorry that I can't share reproducer, but as I said, that would require all the whopping Android build and believe me, you don't want this. I suspect that this issue can be reproduced by firing lots of interrupts simultaneously in kvmtool. And of course in this case there is nothing Xen-specific, so KVM as L1 hypervisor should be fine too. But I have no time to verify this. --=20 WBR, Volodymyr=