From: Corneliu ZUZU <czuzu@bitdefender.com> To: Julien Grall <julien.grall@arm.com>, xen-devel@lists.xen.org Cc: Andre Przywara <andre.przywara@arm.com>, Stefano Stabellini <sstabellini@kernel.org>, Tamas K Lengyel <tamas@tklengyel.com>, Razvan Cojocaru <rcojocaru@bitdefender.com>, Steve Capper <Steve.Capper@arm.com> Subject: Re: [PATCH 7/7] vm-event/arm: implement support for control-register write vm-events Date: Wed, 22 Jun 2016 21:39:19 +0300 [thread overview] Message-ID: <bec2a63f-ec61-6fbe-ee47-4869c86018d5@bitdefender.com> (raw) In-Reply-To: <576AC834.2010701@arm.com> On 6/22/2016 8:17 PM, Julien Grall wrote: > On 22/06/16 17:35, Corneliu ZUZU wrote: > >> Julien, > > Hello Corneliu, > >> I was trying to implement having HCR stored in arch_domain or arch_vcpu >> as suggested above and I'm a bit confused about the code in >> p2m_restore_state. >> I'm hoping you can provide some feedback on this matter. Here's the >> current implementation of the function: >> >> void p2m_restore_state(struct vcpu *n) >> { >> register_t hcr; >> >> hcr = READ_SYSREG(HCR_EL2); >> WRITE_SYSREG(hcr & ~HCR_VM, HCR_EL2); >> isb(); >> >> p2m_load_VTTBR(n->domain); >> isb(); >> >> if ( is_32bit_domain(n->domain) ) >> hcr &= ~HCR_RW; >> else >> hcr |= HCR_RW; >> >> WRITE_SYSREG(n->arch.sctlr, SCTLR_EL1); >> isb(); >> >> WRITE_SYSREG(hcr, HCR_EL2); >> isb(); >> } >> >> First of all, I see the HCR_VM bit being unset (=0) but I don't quite >> understand why and even more peculiar is the fact that I couldn't find >> any place where the bit is set (=1) again. > > After the first write to HCR_EL2, "hcr" still have the VM bit set as > we only mask it. So the second write will re-set the VM bit. > Ooh..right. Don't know how I missed that, I guess I was too focused in finding a -different- place where HCR was modified. > I am not sure why the VM bit is unset/set in this function. I am not > able to find a paragraph justifying it in the ARM ARM. I have CCed > some ARM folks to check if I missed something. > An answer to that would be useful. I'm also curious if there's a reason why HCR_RW is set/unset afterwards and not before and why there's an isb() after calling p2m_load_VTTBR if that function already has an isb() @ its end. >> Secondly, why this order of operations? More specifically, why is >> p2m_load_VTTBR done after the HCR_VM bit is unset and before the HCR_RW >> bit is set/unset? Can't we write HCR only once here? >> And finally, I see the function is called by construct_dom0. The code >> there looks like: >> >> /* >> * The following loads use the domain's p2m and require current to >> * be a vcpu of the domain, temporarily switch >> */ >> saved_current = current; >> p2m_restore_state(v); >> [...] >> /* Now that we are done restore the original p2m and current. */ >> set_current(saved_current); >> p2m_restore_state(saved_current); >> >> I suppose the significant changes p2m_restore_state does for the code in >> between ("[...]") is setting VTTBR & SCTLR which are used by translation >> functions such as gvirt_to_maddr (which seems to use PAR_EL1). >> What I don't grasp is what effect setting the VTTBR has if HCR.HCR_VM is >> unset and left unset... > > HCR.VM is not left unset (see why above). > > Regards, > Thanks, Corneliu. _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-06-22 18:39 UTC|newest] Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-06-16 14:04 [PATCH 0/7] vm-event: Implement ARM support for control-register writes Corneliu ZUZU 2016-06-16 14:06 ` [PATCH 1/7] minor (formatting) fixes Corneliu ZUZU 2016-06-16 14:24 ` Jan Beulich 2016-06-16 19:19 ` Corneliu ZUZU 2016-06-17 7:06 ` Jan Beulich 2016-06-17 10:46 ` Corneliu ZUZU 2016-06-16 16:02 ` Tamas K Lengyel 2016-06-17 8:33 ` Corneliu ZUZU 2016-06-17 8:36 ` Razvan Cojocaru 2016-06-17 9:29 ` Andrew Cooper 2016-06-17 9:35 ` Jan Beulich 2016-06-17 9:33 ` Jan Beulich 2016-06-17 9:36 ` Razvan Cojocaru 2016-06-17 9:40 ` Jan Beulich 2016-06-17 9:42 ` Razvan Cojocaru 2016-06-17 19:05 ` Tamas K Lengyel 2016-06-16 14:07 ` [PATCH 2/7] vm-event: VM_EVENT_FLAG_DENY requires VM_EVENT_FLAG_VCPU_PAUSED Corneliu ZUZU 2016-06-16 16:11 ` Tamas K Lengyel 2016-06-17 8:43 ` Corneliu ZUZU 2016-06-21 11:26 ` Corneliu ZUZU 2016-06-21 15:09 ` Tamas K Lengyel 2016-06-22 8:34 ` Corneliu ZUZU 2016-06-16 14:08 ` [PATCH 3/7] vm-event: introduce vm_event_vcpu_enter Corneliu ZUZU 2016-06-16 14:51 ` Jan Beulich 2016-06-16 20:10 ` Corneliu ZUZU 2016-06-16 20:33 ` Razvan Cojocaru 2016-06-17 10:41 ` Corneliu ZUZU 2016-06-17 7:17 ` Jan Beulich 2016-06-17 11:13 ` Corneliu ZUZU 2016-06-17 11:27 ` Jan Beulich 2016-06-17 12:13 ` Corneliu ZUZU 2016-06-16 16:17 ` Tamas K Lengyel 2016-06-17 9:19 ` Corneliu ZUZU 2016-06-17 8:55 ` Julien Grall 2016-06-17 11:40 ` Corneliu ZUZU 2016-06-17 13:22 ` Julien Grall 2016-06-16 14:09 ` [PATCH 4/7] vm-event/x86: use vm_event_vcpu_enter properly Corneliu ZUZU 2016-06-16 15:00 ` Jan Beulich 2016-06-16 20:20 ` Corneliu ZUZU 2016-06-17 7:20 ` Jan Beulich 2016-06-17 11:23 ` Corneliu ZUZU 2016-06-16 16:27 ` Tamas K Lengyel 2016-06-17 9:24 ` Corneliu ZUZU 2016-06-16 14:10 ` [PATCH 5/7] x86: replace monitor_write_data.do_write with enum Corneliu ZUZU 2016-06-16 14:12 ` [PATCH 6/7] vm-event/arm: move hvm_event_cr->common vm_event_monitor_cr Corneliu ZUZU 2016-06-16 15:16 ` Jan Beulich 2016-06-17 8:25 ` Corneliu ZUZU 2016-06-17 8:38 ` Jan Beulich 2016-06-17 11:31 ` Corneliu ZUZU 2016-06-21 7:08 ` Corneliu ZUZU 2016-06-21 7:20 ` Jan Beulich 2016-06-21 15:22 ` Tamas K Lengyel 2016-06-22 6:33 ` Jan Beulich 2016-06-16 16:55 ` Tamas K Lengyel 2016-06-17 10:37 ` Corneliu ZUZU 2016-06-16 14:13 ` [PATCH 7/7] vm-event/arm: implement support for control-register write vm-events Corneliu ZUZU 2016-06-16 14:26 ` Julien Grall 2016-06-16 19:24 ` Corneliu ZUZU 2016-06-16 21:28 ` Julien Grall 2016-06-17 11:46 ` Corneliu ZUZU 2016-06-16 16:49 ` Julien Grall 2016-06-17 10:36 ` Corneliu ZUZU 2016-06-17 13:18 ` Julien Grall 2016-06-22 16:35 ` Corneliu ZUZU 2016-06-22 17:17 ` Julien Grall 2016-06-22 18:39 ` Corneliu ZUZU [this message] 2016-06-22 19:37 ` Corneliu ZUZU 2016-06-22 19:41 ` Julien Grall 2016-06-23 5:31 ` Corneliu ZUZU 2016-06-23 5:49 ` Corneliu ZUZU 2016-06-23 11:11 ` Julien Grall 2016-06-24 9:32 ` Corneliu ZUZU 2016-06-23 11:00 ` Julien Grall
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