[Devel] [PATCH RHEL7 COMMIT] kvm: Map PFN-type memory regions as writable (if possible)

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.21.1.vz7.50.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.21.1.vz7.47.6
------>
commit 72fc90d2b16a3474d7de8771cecfa80b9a4afd15
Author: KarimAllah Ahmed <karahmed at amazon.de>
Date:   Wed May 16 12:50:47 2018 +0300

    kvm: Map PFN-type memory regions as writable (if possible)
    
    For EPT-violations that are triggered by a read, the pages are also mapped with
    write permissions (if their memory region is also writable). That would avoid
    getting yet another fault on the same page when a write occurs.
    
    This optimization only happens when you have a "struct page" backing the memory
    region. So also enable it for memory regions that do not have a "struct page".
    
    Cc: Paolo Bonzini <pbonzini at redhat.com>
    Cc: Radim Krčmář <rkrcmar at redhat.com>
    Cc: kvm at vger.kernel.org
    Cc: linux-kernel at vger.kernel.org
    Signed-off-by: KarimAllah Ahmed <karahmed at amazon.de>
    Reviewed-by: Paolo Bonzini <pbonzini at redhat.com>
    Signed-off-by: Radim Krčmář <rkrcmar at redhat.com>
    
    (cherry picked from commit a340b3e229b24a56f1c7f5826b15a3af0f4b13e5)
    Signed-off-by: Jan Dakinevich <jan.dakinevich at virtuozzo.com>
    
    =====================
    Patchset description:
    
    EPT fixes and enhancements
    
    Backport of EPT fixes from upstream for
    https://jira.sw.ru/browse/PSBM-84046
    
    Bandan Das (3):
      kvm: mmu: don't set the present bit unconditionally
      kvm: mmu: track read permission explicitly for shadow EPT page tables
      kvm: vmx: advertise support for ept execute only
    
    Junaid Shahid (2):
      kvm: x86: mmu: Use symbolic constants for EPT Violation Exit
        Qualifications
      kvm: x86: mmu: Rename EPT_VIOLATION_READ/WRITE/INSTR constants
    
    KarimAllah Ahmed (2):
      kvm: Map PFN-type memory regions as writable (if possible)
      KVM: x86: Update the exit_qualification access bits while walking an
        address
    
    Paolo Bonzini (5):
      KVM: nVMX: we support 1GB EPT pages
      kvm: x86: MMU support for EPT accessed/dirty bits
      kvm: nVMX: support EPT accessed/dirty bits
      KVM: MMU: return page fault error code from permission_fault
      KVM: nVMX: fix EPT permissions as reported in exit qualification
---
 virt/kvm/kvm_main.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 72de582fc81d..2550415c32fb 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1448,7 +1448,8 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
 
 static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 			       unsigned long addr, bool *async,
-			       bool write_fault, kvm_pfn_t *p_pfn)
+			       bool write_fault, bool *writable,
+			       kvm_pfn_t *p_pfn)
 {
 	unsigned long pfn;
 	int r;
@@ -1470,6 +1471,8 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 
 	}
 
+	if (writable)
+		*writable = true;
 
 	/*
 	 * Get a reference here because callers of *hva_to_pfn* and
@@ -1535,7 +1538,7 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
 	if (vma == NULL)
 		pfn = KVM_PFN_ERR_FAULT;
 	else if (vma->vm_flags & (VM_IO | VM_PFNMAP)) {
-		r = hva_to_pfn_remapped(vma, addr, async, write_fault, &pfn);
+		r = hva_to_pfn_remapped(vma, addr, async, write_fault, writable, &pfn);
 		if (r == -EAGAIN)
 			goto retry;
 		if (r < 0)