From 48599114d3ca24157c25f6684bb9322f6dca12bb Mon Sep 17 00:00:00 2001 From: Anthony PERARD Date: Tue, 26 Nov 2019 14:16:09 +0100 Subject: [PATCH] x86/domctl: have XEN_DOMCTL_getpageframeinfo3 preemptible This hypercall can take a long time to finish because it attempts to grab the `hostp2m' lock up to 1024 times. The accumulated wait for the lock can take several seconds. This can easily happen with a guest with 32 vcpus and plenty of RAM, during localhost migration. While the patch doesn't fix the problem with the lock contention and the fact that the `hostp2m' lock is currently global (and not on a single page), it is still an improvement to the hypercall. It will in particular, down the road, allow dropping the arbitrary limit of 1024 entries per request. Signed-off-by: Anthony PERARD Acked-by: Jan Beulich Release-acked-by: Juergen Gross --- xen/arch/x86/domctl.c | 20 ++++++++++++++++++++ xen/include/public/domctl.h | 4 ++++ 2 files changed, 24 insertions(+) diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c index 43e368d63b..b461aadbd6 100644 --- a/xen/arch/x86/domctl.c +++ b/xen/arch/x86/domctl.c @@ -425,6 +425,26 @@ long arch_do_domctl( ret = -EFAULT; break; } + + /* + * Avoid checking for preemption when the `hostp2m' lock isn't + * involve, i.e. non-translated guest, and avoid preemption on + * the last iteration. + */ + if ( paging_mode_translate(d) && + likely((i + 1) < num) && hypercall_preempt_check() ) + { + domctl->u.getpageframeinfo3.num = num - i - 1; + domctl->u.getpageframeinfo3.array.p = + guest_handle + ((i + 1) * width); + if ( __copy_to_guest(u_domctl, domctl, 1) ) + { + ret = -EFAULT; + break; + } + return hypercall_create_continuation(__HYPERVISOR_domctl, + "h", u_domctl); + } } break; diff --git a/xen/include/public/domctl.h b/xen/include/public/domctl.h index a03e80e598..9f2cfd602c 100644 --- a/xen/include/public/domctl.h +++ b/xen/include/public/domctl.h @@ -163,6 +163,10 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_getdomaininfo_t); #define XEN_DOMCTL_PFINFO_LTAB_MASK (0xfU<<28) /* XEN_DOMCTL_getpageframeinfo3 */ +/* + * Both value `num' and `array' may get modified by the hypercall to allow + * preemption. + */ struct xen_domctl_getpageframeinfo3 { /* IN variables. */ uint64_aligned_t num; -- 2.39.5