From: "Murilo Opsfelder Araújo" <muriloo@linux.ibm.com>
To: Fabiano Rosas <farosas@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Cc: kvm-ppc@vger.kernel.org, npiggin@gmail.com
Subject: Re: [PATCH] KVM: PPC: Align pt_regs in kvm_vcpu_arch structure
Date: Fri, 17 Jun 2022 15:24:43 +0000 [thread overview]
Message-ID: <a2378b90-a465-b60c-cc92-616b9c13daea@linux.ibm.com> (raw)
In-Reply-To: <20220525124944.2613333-1-farosas@linux.ibm.com>
Hi, Fabiano.
On 5/25/22 09:49, Fabiano Rosas wrote:
> The H_ENTER_NESTED hypercall receives as second parameter the address
> of a region of memory containing the values for the nested guest
> privileged registers. We currently use the pt_regs structure contained
> within kvm_vcpu_arch for that end.
>
> Most hypercalls that receive a memory address expect that region to
> not cross a 4k page boundary. We would want H_ENTER_NESTED to follow
> the same pattern so this patch ensures the pt_regs structure sits
> within a page.
>
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Is it necessary to explain in the commit message that even though the second
parameter needs to be 4k-aligned, we're aligning pt_regs to 512 bytes so it can
be placed within a 4k boundary because its size is below 512 bytes?
The natural thinking would be aligning it to 4k bytes, which would punch a huge
hole in kvm_vcpu_arch. I think having the explanation of why 512 vs. 4k is
worthwhile mentioning.
> ---
> arch/powerpc/include/asm/kvm_host.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index faf301d0dec0..87eba60f2920 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -519,7 +519,11 @@ struct kvm_vcpu_arch {
> struct kvmppc_book3s_shadow_vcpu *shadow_vcpu;
> #endif
>
> - struct pt_regs regs;
> + /*
> + * This is passed along to the HV via H_ENTER_NESTED. Align to
> + * prevent it crossing a real 4K page.
> + */
> + struct pt_regs regs __aligned(512);
>
> struct thread_fp_state fp;
>
--
Murilo
prev parent reply other threads:[~2022-06-17 15:24 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-25 12:49 [PATCH] KVM: PPC: Align pt_regs in kvm_vcpu_arch structure Fabiano Rosas
2022-06-17 15:24 ` Murilo Opsfelder Araújo [this message]
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