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Subject[PATCH] x86/hyperv: don't use percpu areas for pcpu_flush/pcpu_flush_ex structures
Date
hv_do_hypercall() does virt_to_phys() translation and with some configs
(CONFIG_SLAB) this doesn't work for percpu areas, we pass wrong memory to
hypervisor and get #GP. We could use working slow_virt_to_phys() instead
but doing so kills the performance.

Move pcpu_flush/pcpu_flush_ex structures out of percpu areas and
allocate memory on first call. The additional level of indirection gives
us a small performance penalty, in future we may consider introducing
hypercall functions which avoid virt_to_phys() conversion and cache
physical addresses of pcpu_flush/pcpu_flush_ex structures somewhere.

Reported-by: Simon Xiao <sixiao@microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
- Please cosider this for 4.14.
---
arch/x86/hyperv/mmu.c | 34 ++++++++++++++++++++++++++++------
1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
index 123d9b501108..b8957309bdc4 100644
--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -36,9 +36,9 @@ struct hv_flush_pcpu_ex {
/* Each gva in gva_list encodes up to 4096 pages to flush */
#define HV_TLB_FLUSH_UNIT (4096 * PAGE_SIZE)

-static struct hv_flush_pcpu __percpu *pcpu_flush;
+static struct hv_flush_pcpu __percpu **pcpu_flush;

-static struct hv_flush_pcpu_ex __percpu *pcpu_flush_ex;
+static struct hv_flush_pcpu_ex __percpu **pcpu_flush_ex;

/*
* Fills in gva_list starting from offset. Returns the number of items added.
@@ -102,6 +102,7 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,
const struct flush_tlb_info *info)
{
int cpu, vcpu, gva_n, max_gvas;
+ struct hv_flush_pcpu **flush_pcpu;
struct hv_flush_pcpu *flush;
u64 status = U64_MAX;
unsigned long flags;
@@ -116,7 +117,17 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,

local_irq_save(flags);

- flush = this_cpu_ptr(pcpu_flush);
+ flush_pcpu = this_cpu_ptr(pcpu_flush);
+
+ if (unlikely(!*flush_pcpu))
+ *flush_pcpu = page_address(alloc_page(GFP_ATOMIC));
+
+ flush = *flush_pcpu;
+
+ if (unlikely(!flush)) {
+ local_irq_restore(flags);
+ goto do_native;
+ }

if (info->mm) {
flush->address_space = virt_to_phys(info->mm->pgd);
@@ -173,6 +184,7 @@ static void hyperv_flush_tlb_others_ex(const struct cpumask *cpus,
const struct flush_tlb_info *info)
{
int nr_bank = 0, max_gvas, gva_n;
+ struct hv_flush_pcpu_ex **flush_pcpu;
struct hv_flush_pcpu_ex *flush;
u64 status = U64_MAX;
unsigned long flags;
@@ -187,7 +199,17 @@ static void hyperv_flush_tlb_others_ex(const struct cpumask *cpus,

local_irq_save(flags);

- flush = this_cpu_ptr(pcpu_flush_ex);
+ flush_pcpu = this_cpu_ptr(pcpu_flush_ex);
+
+ if (unlikely(!*flush_pcpu))
+ *flush_pcpu = page_address(alloc_page(GFP_ATOMIC));
+
+ flush = *flush_pcpu;
+
+ if (unlikely(!flush)) {
+ local_irq_restore(flags);
+ goto do_native;
+ }

if (info->mm) {
flush->address_space = virt_to_phys(info->mm->pgd);
@@ -266,7 +288,7 @@ void hyper_alloc_mmu(void)
return;

if (!(ms_hyperv.hints & HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED))
- pcpu_flush = __alloc_percpu(PAGE_SIZE, PAGE_SIZE);
+ pcpu_flush = alloc_percpu(struct hv_flush_pcpu *);
else
- pcpu_flush_ex = __alloc_percpu(PAGE_SIZE, PAGE_SIZE);
+ pcpu_flush_ex = alloc_percpu(struct hv_flush_pcpu_ex *);
}
--
2.13.6
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