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@xxxxxxxxxxxxx>
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
