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tcg/svm: use host cr4 during NPT page table walk

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During a page table walk of TCG+SVM the code in target/i386/excp_helper.c
get_hphys() uses the cr4 register of the guest instead of the hypervisor
to check for the PSE bit. In the test case we have, the guest have not
enabled (yet) the PSE bit and so the page table walk results in a wrong
host physical address resolution and wrong content read by the guest.

Attached patch is against 4.2.1, but works also on 3.1.0. It fixes the
issue for our automated testcase, which is a 32bit hypervisor w/o PAE
support running a guest VM with tcg+svm.

The test worked beforehand up to qemu 2.12, started to fail with qemu 3.0
and later. The added TCG/SVM NPT commit seems to introduce the regression.

In case someone want to try to reproduce it, the iso is at [0], the good
case is [1] and the failing case is [2]. The used commandline is:

qemu-system-i386 -no-kvm -nographic -cpu phenom -m 512 -machine q35 -cdrom seoul-vmm-test.iso

[0] https://depot.genode.org/alex-ab/images/seoul-vmm-test.iso
[1] https://depot.genode.org/alex-ab/images/seoul-vmm-good.txt
[2] https://depot.genode.org/alex-ab/images/seoul-vmm-bad.txt

Signed-off-by: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Alexander Boettcher 2020-06-29 15:25:03 +02:00 committed by Paolo Bonzini
parent 45db94cc90
commit a2d57703b3
3 changed files with 9 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
target/i386/excp_helper.c
View File

@ -262,8 +262,8 @@ static hwaddr get_hphys(CPUState *cs, hwaddr gphys, MMUAccessType access_type,
}
ptep = pde | PG_NX_MASK;
/* if PSE bit is set, then we use a 4MB page */
if ((pde & PG_PSE_MASK) && (env->cr[4] & CR4_PSE_MASK)) {
/* if host cr4 PSE bit is set, then we use a 4MB page */
if ((pde & PG_PSE_MASK) && (env->nested_pg_mode & SVM_NPT_PSE)) {
page_size = 4096 * 1024;
pte_addr = pde_addr;

1
target/i386/svm.h
View File

@ -135,6 +135,7 @@
#define SVM_NPT_PAE (1 << 0)
#define SVM_NPT_LMA (1 << 1)
#define SVM_NPT_NXE (1 << 2)
#define SVM_NPT_PSE (1 << 3)
#define SVM_NPTEXIT_P (1ULL << 0)
#define SVM_NPTEXIT_RW (1ULL << 1)

7
target/i386/svm_helper.c
View File

@ -209,16 +209,21 @@ void helper_vmrun(CPUX86State *env, int aflag, int next_eip_addend)
nested_ctl = x86_ldq_phys(cs, env->vm_vmcb + offsetof(struct vmcb,
control.nested_ctl));
env->nested_pg_mode = 0;
if (nested_ctl & SVM_NPT_ENABLED) {
env->nested_cr3 = x86_ldq_phys(cs,
env->vm_vmcb + offsetof(struct vmcb,
control.nested_cr3));
env->hflags2 |= HF2_NPT_MASK;
env->nested_pg_mode = 0;
if (env->cr[4] & CR4_PAE_MASK) {
env->nested_pg_mode |= SVM_NPT_PAE;
}
if (env->cr[4] & CR4_PSE_MASK) {
env->nested_pg_mode |= SVM_NPT_PSE;
}
if (env->hflags & HF_LMA_MASK) {
env->nested_pg_mode |= SVM_NPT_LMA;
}