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Date: Thu, 11 Jul 2019 08:03:34 -0400
From: Nitesh Narayan Lal <nitesh@...hat.com>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: kvm list <kvm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
linux-mm <linux-mm@...ck.org>,
Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com,
pagupta@...hat.com, wei.w.wang@...el.com,
Yang Zhang <yang.zhang.wz@...il.com>,
Rik van Riel <riel@...riel.com>,
David Hildenbrand <david@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>, dodgen@...gle.com,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
dhildenb@...hat.com, Andrea Arcangeli <aarcange@...hat.com>,
john.starks@...rosoft.com, Dave Hansen <dave.hansen@...el.com>,
Michal Hocko <mhocko@...e.com>
Subject: Re: [QEMU Patch] virtio-baloon: Support for page hinting
On 7/10/19 4:17 PM, Alexander Duyck wrote:
> On Wed, Jul 10, 2019 at 12:53 PM Nitesh Narayan Lal <nitesh@...hat.com> wrote:
>> Enables QEMU to perform madvise free on the memory range reported
>> by the vm.
>>
>> Signed-off-by: Nitesh Narayan Lal <nitesh@...hat.com>
>> ---
>> hw/virtio/trace-events | 1 +
>> hw/virtio/virtio-balloon.c | 59 +++++++++++++++++++
>> include/hw/virtio/virtio-balloon.h | 2 +-
>> include/qemu/osdep.h | 7 +++
>> .../standard-headers/linux/virtio_balloon.h | 1 +
>> 5 files changed, 69 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
>> index e28ba48da6..f703a22d36 100644
>> --- a/hw/virtio/trace-events
>> +++ b/hw/virtio/trace-events
>> @@ -46,6 +46,7 @@ virtio_balloon_handle_output(const char *name, uint64_t gpa) "section name: %s g
>> virtio_balloon_get_config(uint32_t num_pages, uint32_t actual) "num_pages: %d actual: %d"
>> virtio_balloon_set_config(uint32_t actual, uint32_t oldactual) "actual: %d oldactual: %d"
>> virtio_balloon_to_target(uint64_t target, uint32_t num_pages) "balloon target: 0x%"PRIx64" num_pages: %d"
>> +virtio_balloon_hinting_request(unsigned long pfn, unsigned int num_pages) "Guest page hinting request PFN:%lu size: %d"
>>
>> # virtio-mmio.c
>> virtio_mmio_read(uint64_t offset) "virtio_mmio_read offset 0x%" PRIx64
>> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
>> index 2112874055..5d186707b5 100644
>> --- a/hw/virtio/virtio-balloon.c
>> +++ b/hw/virtio/virtio-balloon.c
>> @@ -34,6 +34,9 @@
>>
>> #define BALLOON_PAGE_SIZE (1 << VIRTIO_BALLOON_PFN_SHIFT)
>>
>> +#define VIRTIO_BALLOON_PAGE_HINTING_MAX_PAGES 16
>> +void free_mem_range(uint64_t addr, uint64_t len);
>> +
> The definition you have here is unused. I think you can drop it. Also
> why do you need this forward declaration? Couldn't you just leave
> free_mem_range below as a static and still have this compile?
+1. Thanks for pointing this out.
>
>> struct PartiallyBalloonedPage {
>> RAMBlock *rb;
>> ram_addr_t base;
>> @@ -328,6 +331,58 @@ static void balloon_stats_set_poll_interval(Object *obj, Visitor *v,
>> balloon_stats_change_timer(s, 0);
>> }
>>
>> +void free_mem_range(uint64_t addr, uint64_t len)
>> +{
>> + int ret = 0;
>> + void *hvaddr_to_free;
>> + MemoryRegionSection mrs = memory_region_find(get_system_memory(),
>> + addr, 1);
>> + if (!mrs.mr) {
>> + warn_report("%s:No memory is mapped at address 0x%lu", __func__, addr);
>> + return;
>> + }
>> +
>> + if (!memory_region_is_ram(mrs.mr) && !memory_region_is_romd(mrs.mr)) {
>> + warn_report("%s:Memory at address 0x%s is not RAM:0x%lu", __func__,
>> + HWADDR_PRIx, addr);
>> + memory_region_unref(mrs.mr);
>> + return;
>> + }
>> +
>> + hvaddr_to_free = qemu_map_ram_ptr(mrs.mr->ram_block, mrs.offset_within_region);
>> + trace_virtio_balloon_hinting_request(addr, len);
>> + ret = qemu_madvise(hvaddr_to_free,len, QEMU_MADV_FREE);
>> + if (ret == -1) {
>> + warn_report("%s: Madvise failed with error:%d", __func__, ret);
>> + }
>> +}
>> +
>> +static void virtio_balloon_handle_page_hinting(VirtIODevice *vdev,
>> + VirtQueue *vq)
>> +{
>> + VirtQueueElement *elem;
>> + size_t offset = 0;
>> + uint64_t gpa, len;
>> + elem = virtqueue_pop(vq, sizeof(VirtQueueElement));
>> + if (!elem) {
>> + return;
>> + }
>> + /* For pending hints which are < max_pages(16), 'gpa != 0' ensures that we
>> + * only read the buffer which holds a valid PFN value.
>> + * TODO: Find a better way to do this.
>> + */
> I'm not sure this comment makes much sense to me. Shouldn't the
> iov_to_buf be limiting you anyway? Why do you need the additional gpa
> check?
>
>> + while (iov_to_buf(elem->out_sg, elem->out_num, offset, &gpa, 8) == 8 && gpa != 0) {
>> + offset += 8;
>> + offset += iov_to_buf(elem->out_sg, elem->out_num, offset, &len, 8);
> Why pull this out as two separate buffers? Why not just define a
> structure that consists of the two uint64_t values and then pull the
> entire thing as one buffer?
This does make sense. I will correct this. Thanks.
> I'm pretty sure the solution as you have
> it now opens you up to an error since you could have a malicious guest
> only give you a part of the structure and you really should be
> verifying you get the entire structure.
>
>> + if (!qemu_balloon_is_inhibited()) {
>> + free_mem_range(gpa, len);
>> + }
>> + }
>> + virtqueue_push(vq, elem, offset);
>> + virtio_notify(vdev, vq);
>> + g_free(elem);
>> +}
>> +
>> static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>> {
>> VirtIOBalloon *s = VIRTIO_BALLOON(vdev);
>> @@ -694,6 +749,7 @@ static uint64_t virtio_balloon_get_features(VirtIODevice *vdev, uint64_t f,
>> VirtIOBalloon *dev = VIRTIO_BALLOON(vdev);
>> f |= dev->host_features;
>> virtio_add_feature(&f, VIRTIO_BALLOON_F_STATS_VQ);
>> + virtio_add_feature(&f, VIRTIO_BALLOON_F_HINTING);
>>
>> return f;
>> }
>> @@ -780,6 +836,7 @@ static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
>> s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>> s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>> s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
>> + s->hvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_page_hinting);
>>
>> if (virtio_has_feature(s->host_features,
>> VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
>> @@ -875,6 +932,8 @@ static void virtio_balloon_instance_init(Object *obj)
>>
>> object_property_add(obj, "guest-stats", "guest statistics",
>> balloon_stats_get_all, NULL, NULL, s, NULL);
>> + object_property_add(obj, "guest-page-hinting", "guest page hinting",
>> + NULL, NULL, NULL, s, NULL);
>>
>> object_property_add(obj, "guest-stats-polling-interval", "int",
>> balloon_stats_get_poll_interval,
>> diff --git a/include/hw/virtio/virtio-balloon.h b/include/hw/virtio/virtio-balloon.h
>> index 1afafb12f6..a58b24fdf2 100644
>> --- a/include/hw/virtio/virtio-balloon.h
>> +++ b/include/hw/virtio/virtio-balloon.h
>> @@ -44,7 +44,7 @@ enum virtio_balloon_free_page_report_status {
>>
>> typedef struct VirtIOBalloon {
>> VirtIODevice parent_obj;
>> - VirtQueue *ivq, *dvq, *svq, *free_page_vq;
>> + VirtQueue *ivq, *dvq, *svq, *free_page_vq, *hvq;
>> uint32_t free_page_report_status;
>> uint32_t num_pages;
>> uint32_t actual;
>> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
>> index af2b91f0b8..bb9207e7f4 100644
>> --- a/include/qemu/osdep.h
>> +++ b/include/qemu/osdep.h
>> @@ -360,6 +360,11 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>> #else
>> #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>> #endif
>> +#ifdef MADV_FREE
>> +#define QEMU_MADV_FREE MADV_FREE
>> +#else
>> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
>> +#endif
> As I mentioned before it might make more sense to use MADV_DONTNEED
> instead of just disabling this functionality if the host kernel
> doesn't have MADV_FREE support.
I have been trying to find the reason for it and later decided to just
avoid hinting and print an error message instead.
> That way you would still have the
> functionality on kernels prior to 4.5 if they need it.
I didn't think of this earlier. If that's the case it does make sense
fallback to DONTNEED.
>
>> #elif defined(CONFIG_POSIX_MADVISE)
>>
>> @@ -373,6 +378,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>> #define QEMU_MADV_HUGEPAGE QEMU_MADV_INVALID
>> #define QEMU_MADV_NOHUGEPAGE QEMU_MADV_INVALID
>> #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
> Same here. It might make more sense to use the POSIX_MADV_DONTNEED
> instead of just making it invalid.
>
>> #else /* no-op */
>>
>> @@ -386,6 +392,7 @@ void qemu_anon_ram_free(void *ptr, size_t size);
>> #define QEMU_MADV_HUGEPAGE QEMU_MADV_INVALID
>> #define QEMU_MADV_NOHUGEPAGE QEMU_MADV_INVALID
>> #define QEMU_MADV_REMOVE QEMU_MADV_INVALID
>> +#define QEMU_MADV_FREE QEMU_MADV_INVALID
>>
>> #endif
>>
>> diff --git a/include/standard-headers/linux/virtio_balloon.h b/include/standard-headers/linux/virtio_balloon.h
>> index 9375ca2a70..f9e3e82562 100644
>> --- a/include/standard-headers/linux/virtio_balloon.h
>> +++ b/include/standard-headers/linux/virtio_balloon.h
>> @@ -36,6 +36,7 @@
>> #define VIRTIO_BALLOON_F_DEFLATE_ON_OOM 2 /* Deflate balloon on OOM */
>> #define VIRTIO_BALLOON_F_FREE_PAGE_HINT 3 /* VQ to report free pages */
>> #define VIRTIO_BALLOON_F_PAGE_POISON 4 /* Guest is using page poisoning */
>> +#define VIRTIO_BALLOON_F_HINTING 5 /* Page hinting virtqueue */
>>
>> /* Size of a PFN in the balloon interface. */
>> #define VIRTIO_BALLOON_PFN_SHIFT 12
>> --
>> 2.21.0
>>
--
Thanks
Nitesh
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