[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH] x86/cpu: revert opt_allow_unsafe from __ro_after_init to __read_mostly
On Mon, Sep 02, 2024 at 05:16:05PM +0200, Jan Beulich wrote: > On 02.09.2024 17:00, Roger Pau Monne wrote: > > Making opt_allow_unsafe read only after init requires changes to the logic > > in > > init_amd(), otherwise the following #PF happens on CPU hotplug: > > > > ----[ Xen-4.20.0-1-d x86_64 debug=y Tainted: H ]---- > > CPU: 1 > > RIP: e008:[<ffff82d040291081>] arch/x86/cpu/amd.c#init_amd+0x37f/0x993 > > [...] > > Xen call trace: > > [<ffff82d040291081>] R arch/x86/cpu/amd.c#init_amd+0x37f/0x993 > > [<ffff82d040291fbe>] F identify_cpu+0x2d4/0x4db > > [<ffff82d04032eeaa>] F start_secondary+0x22e/0x3cf > > [<ffff82d040203327>] F __high_start+0x87/0xa0 > > > > Pagetable walk from ffff82d0404011ea: > > L4[0x105] = 000000006fc2e063 ffffffffffffffff > > L3[0x141] = 000000006fc2b063 ffffffffffffffff > > L2[0x002] = 000000807c7ca063 ffffffffffffffff > > L1[0x001] = 800000006f801121 ffffffffffffffff > > > > **************************************** > > Panic on CPU 1: > > FATAL PAGE FAULT > > [error_code=0003] > > Faulting linear address: ffff82d0404011ea > > **************************************** > > Hmm, I specifically looked at that code, but I can see how I screwed up. > > > For the time being revert opt_allow_unsafe to be __read_mostly. > > There's exactly one write that an AP can hit. Is it really worth moving > back, rather than just doing > > if (opt_allow_unsafe <= 0 && !cpu_has_amd_erratum(c, AMD_ERRATUM_121)) > opt_allow_unsafe = 1; > else if ... > > ? I would rather move this logic so it's only the BSP that can set opt_allow_unsafe, and the APs check they match the configuration set by the BSP. I think the resulting logic would be cleaner, but I didn't want to do such a change as part of this fix. Thanks, Roger.
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