| Message ID | 1505128612-13819-1-git-send-email-gengdongjiu@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 11/09/17 12:16, Dongjiu Geng wrote: > PSTATE.PAN disables reading and/or writing to a userspace virtual > address from EL1 in non-VHE or from EL2 in VHE. In non-VHE, there is > no any userspace mapping at EL2, so no need to reest the PSTATE.PAN. ^^^^^ reset > > Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com> > Signed-off-by: Haibin Zhang <zhanghaibin7@huawei.com> > --- > arch/arm64/kvm/hyp/entry.S | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index 12ee62d6d410..86a7549b1b4c 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -96,8 +96,12 @@ ENTRY(__guest_exit) > > add x1, x1, #VCPU_CONTEXT > > - ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > + b 2f // skip PAN at EL2 in non-VHE > +alternative_else_nop_endif > > + ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > +2: > // Store the guest regs x2 and x3 > stp x2, x3, [x1, #CPU_XREG_OFFSET(2)] > > Ok. Probably I need to say why original patch did not consider non-VHE case: - VHE and PAN features come within the same v8.1 extension bundle, so it is unlucky to see IRL implementation with PAN but no VHE. - Given above the only case where extra PAN instruction could count is VHE-enabled system with CONFIG_ARM64_VHE is not set; However, IMO, usecase for such setup is kind of debugging; it is quite obvious that those who care of performance should not disable VHE in the first place... Nit: In general it is not polite to keep posting patches in a middle of the merge window - people are busy with more important stuff... Cheers Vladimir
Hi Vladimir, On 2017/9/11 19:20, Vladimir Murzin wrote: > On 11/09/17 12:16, Dongjiu Geng wrote: >> PSTATE.PAN disables reading and/or writing to a userspace virtual >> address from EL1 in non-VHE or from EL2 in VHE. In non-VHE, there is >> no any userspace mapping at EL2, so no need to reest the PSTATE.PAN. > ^^^^^ > reset >> >> Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com> >> Signed-off-by: Haibin Zhang <zhanghaibin7@huawei.com> >> --- >> arch/arm64/kvm/hyp/entry.S | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S >> index 12ee62d6d410..86a7549b1b4c 100644 >> --- a/arch/arm64/kvm/hyp/entry.S >> +++ b/arch/arm64/kvm/hyp/entry.S >> @@ -96,8 +96,12 @@ ENTRY(__guest_exit) >> >> add x1, x1, #VCPU_CONTEXT >> >> - ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) >> +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN >> + b 2f // skip PAN at EL2 in non-VHE >> +alternative_else_nop_endif >> >> + ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) >> +2: >> // Store the guest regs x2 and x3 >> stp x2, x3, [x1, #CPU_XREG_OFFSET(2)] >> >> > > Ok. Probably I need to say why original patch did not consider non-VHE case: > - VHE and PAN features come within the same v8.1 extension bundle, so it is > unlucky to see IRL implementation with PAN but no VHE. > - Given above the only case where extra PAN instruction could count is > VHE-enabled system with CONFIG_ARM64_VHE is not set; However, IMO, usecase for > such setup is kind of debugging; it is quite obvious that those who care of > performance should not disable VHE in the first place... thanks for the explanation. > > Nit: > In general it is not polite to keep posting patches in a middle of the merge > window - people are busy with more important stuff... I do not know when you are busy and in merge window > > Cheers > Vladimir > > . >
On Mon, Sep 11 2017 at 7:48:45 pm BST, gengdongjiu <gengdongjiu@huawei.com> wrote: > Hi Vladimir, > > [...] >> Nit: >> In general it is not polite to keep posting patches in a middle of the merge >> window - people are busy with more important stuff... > I do not know when you are busy and in merge window But maybe it is about time you find out how we work if you intend to be a part of this community. A number of your colleagues (such as Hanjun Guo, which I've now cc'd) are perfectly aware of the kernel merge process and you could probably learn from talking to him. Thanks, M.
On Mon, Sep 11 2017 at 7:16:52 pm BST, Dongjiu Geng <gengdongjiu@huawei.com> wrote: > PSTATE.PAN disables reading and/or writing to a userspace virtual > address from EL1 in non-VHE or from EL2 in VHE. In non-VHE, there is > no any userspace mapping at EL2, so no need to reest the PSTATE.PAN. > > Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com> > Signed-off-by: Haibin Zhang <zhanghaibin7@huawei.com> > --- > arch/arm64/kvm/hyp/entry.S | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S > index 12ee62d6d410..86a7549b1b4c 100644 > --- a/arch/arm64/kvm/hyp/entry.S > +++ b/arch/arm64/kvm/hyp/entry.S > @@ -96,8 +96,12 @@ ENTRY(__guest_exit) > > add x1, x1, #VCPU_CONTEXT > > - ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN > + b 2f // skip PAN at EL2 in non-VHE > +alternative_else_nop_endif > > + ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) > +2: > // Store the guest regs x2 and x3 > stp x2, x3, [x1, #CPU_XREG_OFFSET(2)] Aside from Vladimir's comment about why this may not be an important change in practice (both features are v8.1, and expected to be implemented at the same time as VHE), I'm not sure this brings us much. We're just trading a write to PSTATE (which will have no effect other than storing a bit in PSTATE) for a branch, and I'm not sure what is the worse. Your patch definitely makes the code less readable, and I value ease of maintenance very much. Do you have any data coming from a non-VHE, PAN-enabled system that shows a measurable, significant performance improvement with this patch? Because that would be the only reason why I'd consider such a change. Thanks, M.
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S index 12ee62d6d410..86a7549b1b4c 100644 --- a/arch/arm64/kvm/hyp/entry.S +++ b/arch/arm64/kvm/hyp/entry.S @@ -96,8 +96,12 @@ ENTRY(__guest_exit) add x1, x1, #VCPU_CONTEXT - ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) +alternative_if_not ARM64_HAS_VIRT_HOST_EXTN + b 2f // skip PAN at EL2 in non-VHE +alternative_else_nop_endif + ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN) +2: // Store the guest regs x2 and x3 stp x2, x3, [x1, #CPU_XREG_OFFSET(2)]