| Message ID | 53F30FCD.3080109@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Il 19/08/2014 10:50, Xiao Guangrong ha scritto: > Okay, what confused me it that it seems that the single line patch > is ok to you. :) No, it was late and I was confused. :) > Now, do we really need to care the case 2? like David said: > "Sorry I didn't explain myself very well: Since we can get a single wrong > mmio exit no matter what, it has to be handled in userspace. So my point > was, it doesn't really help to fix that one very specific way that it can > happen, because it can just happen in other ways. (E.g. update memslots > occurs after is_noslot_pfn() and before mmio exit)." > > What's your idea? > > > I think if you always treat the low bit as zero in mmio sptes, you can > > do that without losing a bit of the generation. > > What's you did is avoiding cache a invalid generation number into spte, but > actually if we can figure it out when we check mmio access, it's ok. Like the > updated patch i posted should fix it, that way avoids doubly increase the number. Yes. > Okay, if you're interested increasing the number doubly, there is the simpler > one: This wastes a bit in the mmio spte though. My idea is to increase the memslots generation twice, but drop the low bit in the mmio spte. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 08/19/2014 05:03 PM, Paolo Bonzini wrote: > Il 19/08/2014 10:50, Xiao Guangrong ha scritto: >> Okay, what confused me it that it seems that the single line patch >> is ok to you. :) > > No, it was late and I was confused. :) > >> Now, do we really need to care the case 2? like David said: >> "Sorry I didn't explain myself very well: Since we can get a single wrong >> mmio exit no matter what, it has to be handled in userspace. So my point >> was, it doesn't really help to fix that one very specific way that it can >> happen, because it can just happen in other ways. (E.g. update memslots >> occurs after is_noslot_pfn() and before mmio exit)." >> >> What's your idea? >> >>> I think if you always treat the low bit as zero in mmio sptes, you can >>> do that without losing a bit of the generation. >> >> What's you did is avoiding cache a invalid generation number into spte, but >> actually if we can figure it out when we check mmio access, it's ok. Like the >> updated patch i posted should fix it, that way avoids doubly increase the number. > > Yes. > >> Okay, if you're interested increasing the number doubly, there is the simpler >> one: > > This wastes a bit in the mmio spte though. My idea is to increase the > memslots generation twice, but drop the low bit in the mmio spte. Yeah, really smart idea. :) Paolo/David, would you mind making a patch for this (+ the comments in David's patch)? Please feel free to add my: Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Aug 19, 2014 at 5:29 PM, Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> wrote: > On 08/19/2014 05:03 PM, Paolo Bonzini wrote: >> Il 19/08/2014 10:50, Xiao Guangrong ha scritto: >>> Okay, what confused me it that it seems that the single line patch >>> is ok to you. :) >> >> No, it was late and I was confused. :) >> >>> Now, do we really need to care the case 2? like David said: >>> "Sorry I didn't explain myself very well: Since we can get a single wrong >>> mmio exit no matter what, it has to be handled in userspace. So my point >>> was, it doesn't really help to fix that one very specific way that it can >>> happen, because it can just happen in other ways. (E.g. update memslots >>> occurs after is_noslot_pfn() and before mmio exit)." >>> >>> What's your idea? >>> >>>> I think if you always treat the low bit as zero in mmio sptes, you can >>>> do that without losing a bit of the generation. >>> >>> What's you did is avoiding cache a invalid generation number into spte, but >>> actually if we can figure it out when we check mmio access, it's ok. Like the >>> updated patch i posted should fix it, that way avoids doubly increase the number. >> >> Yes. >> >>> Okay, if you're interested increasing the number doubly, there is the simpler >>> one: >> >> This wastes a bit in the mmio spte though. My idea is to increase the >> memslots generation twice, but drop the low bit in the mmio spte. > > Yeah, really smart idea. :) > > Paolo/David, would you mind making a patch for this (+ the comments in David's > patch)? Paolo, since it was your idea would you like to write it? I don't mind either way. > > Please feel free to add my: > Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Il 20/08/2014 03:03, David Matlack ha scritto: > On Tue, Aug 19, 2014 at 5:29 PM, Xiao Guangrong > <xiaoguangrong@linux.vnet.ibm.com> wrote: >> On 08/19/2014 05:03 PM, Paolo Bonzini wrote: >>> Il 19/08/2014 10:50, Xiao Guangrong ha scritto: >>>> Okay, what confused me it that it seems that the single line patch >>>> is ok to you. :) >>> >>> No, it was late and I was confused. :) >>> >>>> Now, do we really need to care the case 2? like David said: >>>> "Sorry I didn't explain myself very well: Since we can get a single wrong >>>> mmio exit no matter what, it has to be handled in userspace. So my point >>>> was, it doesn't really help to fix that one very specific way that it can >>>> happen, because it can just happen in other ways. (E.g. update memslots >>>> occurs after is_noslot_pfn() and before mmio exit)." >>>> >>>> What's your idea? >>>> >>>>> I think if you always treat the low bit as zero in mmio sptes, you can >>>>> do that without losing a bit of the generation. >>>> >>>> What's you did is avoiding cache a invalid generation number into spte, but >>>> actually if we can figure it out when we check mmio access, it's ok. Like the >>>> updated patch i posted should fix it, that way avoids doubly increase the number. >>> >>> Yes. >>> >>>> Okay, if you're interested increasing the number doubly, there is the simpler >>>> one: >>> >>> This wastes a bit in the mmio spte though. My idea is to increase the >>> memslots generation twice, but drop the low bit in the mmio spte. >> >> Yeah, really smart idea. :) >> >> Paolo/David, would you mind making a patch for this (+ the comments in David's >> patch)? > > Paolo, since it was your idea would you like to write it? I don't mind either > way. Sure, I'll post the patch for review. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 9314678..bf49170 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -236,6 +236,9 @@ static unsigned int get_mmio_spte_generation(u64 spte) static unsigned int kvm_current_mmio_generation(struct kvm *kvm) { + /* The initialized generation number should be even. */ + BUILD_BUG_ON((MMIO_MAX_GEN - 150) & 0x1); + /* * Init kvm generation close to MMIO_MAX_GEN to easily test the * code of handling generation number wrap-around. @@ -292,6 +295,14 @@ static bool check_mmio_spte(struct kvm *kvm, u64 spte) kvm_gen = kvm_current_mmio_generation(kvm); spte_gen = get_mmio_spte_generation(spte); + /* + * Aha, we cached a being-updated generation number or + * generation number is currnetly being updated, let do the + * real check for mmio access. + */ + if ((kvm_gen | spte_gen) & 0x1) + return false; + trace_check_mmio_spte(spte, kvm_gen, spte_gen); return likely(kvm_gen == spte_gen); } diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 33712fb..5c3f7b7 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -725,7 +725,7 @@ static struct kvm_memslots *install_new_memslots(struct kvm *kvm, update_memslots(slots, new, kvm->memslots->generation); rcu_assign_pointer(kvm->memslots, slots); synchronize_srcu_expedited(&kvm->srcu); - + kvm->memslots->generation++; kvm_arch_memslots_updated(kvm); return old_memslots;