From 67f4f663cd6179d57f3e5a558f1526c7dc8c6742 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 14 Feb 2024 16:17:00 +0100 Subject: [PATCH] libvhost-user: Dynamically remap rings after (temporarily?) removing memory regions Currently, we try to remap all rings whenever we add a single new memory region. That doesn't quite make sense, because we already map rings when setting the ring address, and panic if that goes wrong. Likely, that handling was simply copied from set_mem_table code, where we actually have to remap all rings. Remapping all rings might require us to walk quite a lot of memory regions to perform the address translations. Ideally, we'd simply remove that remapping. However, let's be a bit careful. There might be some weird corner cases where we might temporarily remove a single memory region (e.g., resize it), that would have worked for now. Further, a ring might be located on hotplugged memory, and as the VM reboots, we might unplug that memory, to hotplug memory before resetting the ring addresses. So let's unmap affected rings as we remove a memory region, and try dynamically mapping the ring again when required. Acked-by: Raphael Norwitz Acked-by: Stefano Garzarella Signed-off-by: David Hildenbrand Message-Id: <20240214151701.29906-14-david@redhat.com> Tested-by: Mario Casquero Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- subprojects/libvhost-user/libvhost-user.c | 107 ++++++++++++++++------ 1 file changed, 78 insertions(+), 29 deletions(-) diff --git a/subprojects/libvhost-user/libvhost-user.c b/subprojects/libvhost-user/libvhost-user.c index ed0a978d4f..61fb3050b3 100644 --- a/subprojects/libvhost-user/libvhost-user.c +++ b/subprojects/libvhost-user/libvhost-user.c @@ -283,10 +283,75 @@ vu_remove_all_mem_regs(VuDev *dev) dev->nregions = 0; } +static bool +map_ring(VuDev *dev, VuVirtq *vq) +{ + vq->vring.desc = qva_to_va(dev, vq->vra.desc_user_addr); + vq->vring.used = qva_to_va(dev, vq->vra.used_user_addr); + vq->vring.avail = qva_to_va(dev, vq->vra.avail_user_addr); + + DPRINT("Setting virtq addresses:\n"); + DPRINT(" vring_desc at %p\n", vq->vring.desc); + DPRINT(" vring_used at %p\n", vq->vring.used); + DPRINT(" vring_avail at %p\n", vq->vring.avail); + + return !(vq->vring.desc && vq->vring.used && vq->vring.avail); +} + static bool vu_is_vq_usable(VuDev *dev, VuVirtq *vq) { - return likely(!dev->broken) && likely(vq->vring.avail); + if (unlikely(dev->broken)) { + return false; + } + + if (likely(vq->vring.avail)) { + return true; + } + + /* + * In corner cases, we might temporarily remove a memory region that + * mapped a ring. When removing a memory region we make sure to + * unmap any rings that would be impacted. Let's try to remap if we + * already succeeded mapping this ring once. + */ + if (!vq->vra.desc_user_addr || !vq->vra.used_user_addr || + !vq->vra.avail_user_addr) { + return false; + } + if (map_ring(dev, vq)) { + vu_panic(dev, "remapping queue on access"); + return false; + } + return true; +} + +static void +unmap_rings(VuDev *dev, VuDevRegion *r) +{ + int i; + + for (i = 0; i < dev->max_queues; i++) { + VuVirtq *vq = &dev->vq[i]; + const uintptr_t desc = (uintptr_t)vq->vring.desc; + const uintptr_t used = (uintptr_t)vq->vring.used; + const uintptr_t avail = (uintptr_t)vq->vring.avail; + + if (desc < r->mmap_addr || desc >= r->mmap_addr + r->size) { + continue; + } + if (used < r->mmap_addr || used >= r->mmap_addr + r->size) { + continue; + } + if (avail < r->mmap_addr || avail >= r->mmap_addr + r->size) { + continue; + } + + DPRINT("Unmapping rings of queue %d\n", i); + vq->vring.desc = NULL; + vq->vring.used = NULL; + vq->vring.avail = NULL; + } } static size_t @@ -786,21 +851,6 @@ vu_reset_device_exec(VuDev *dev, VhostUserMsg *vmsg) return false; } -static bool -map_ring(VuDev *dev, VuVirtq *vq) -{ - vq->vring.desc = qva_to_va(dev, vq->vra.desc_user_addr); - vq->vring.used = qva_to_va(dev, vq->vra.used_user_addr); - vq->vring.avail = qva_to_va(dev, vq->vra.avail_user_addr); - - DPRINT("Setting virtq addresses:\n"); - DPRINT(" vring_desc at %p\n", vq->vring.desc); - DPRINT(" vring_used at %p\n", vq->vring.used); - DPRINT(" vring_avail at %p\n", vq->vring.avail); - - return !(vq->vring.desc && vq->vring.used && vq->vring.avail); -} - static bool generate_faults(VuDev *dev) { unsigned int i; @@ -884,7 +934,6 @@ generate_faults(VuDev *dev) { static bool vu_add_mem_reg(VuDev *dev, VhostUserMsg *vmsg) { - int i; VhostUserMemoryRegion m = vmsg->payload.memreg.region, *msg_region = &m; if (vmsg->fd_num != 1) { @@ -930,19 +979,9 @@ vu_add_mem_reg(VuDev *dev, VhostUserMsg *vmsg) { vmsg->fd_num = 0; DPRINT("Successfully added new region in postcopy\n"); return true; - } else { - for (i = 0; i < dev->max_queues; i++) { - if (dev->vq[i].vring.desc) { - if (map_ring(dev, &dev->vq[i])) { - vu_panic(dev, "remapping queue %d for new memory region", - i); - } - } - } - - DPRINT("Successfully added new region\n"); - return false; } + DPRINT("Successfully added new region\n"); + return false; } static inline bool reg_equal(VuDevRegion *vudev_reg, @@ -995,6 +1034,16 @@ vu_rem_mem_reg(VuDev *dev, VhostUserMsg *vmsg) { return false; } + /* + * There might be valid cases where we temporarily remove memory regions + * to readd them again, or remove memory regions and don't use the rings + * anymore before we set the ring addresses and restart the device. + * + * Unmap all affected rings, remapping them on demand later. This should + * be a corner case. + */ + unmap_rings(dev, r); + munmap((void *)(uintptr_t)r->mmap_addr, r->size + r->mmap_offset); idx = r - dev->regions;