| Message ID | 20200602164911.5706-1-alex.bennee@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [RFC] exec: flush the whole TLB if a watchpoint crosses a page boundary | expand |
On 6/2/20 9:49 AM, Alex Bennée wrote: > There is no particular reason why you can't have a watchpoint in TCG > that covers a large chunk of the address space. We could be clever > about it but these cases are pretty rare and we can assume the user > will expect a little performance degradation. > > NB: In my testing gdb will silently squash a watchpoint like: > > watch (char[0x7fffffffff]) *0x0 > > to a 4 byte watchpoint. Practically it will limit the maximum size > based on max-value-size. However given enough of a tweak the sky is > the limit. > > Reported-by: Alexander Bulekov <alxndr@bu.edu> > Signed-off-by: Alex Bennée <alex.bennee@linaro.org> > --- > exec.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/exec.c b/exec.c > index 5162f0d12f9..851ac180fe7 100644 > --- a/exec.c > +++ b/exec.c > @@ -1056,7 +1056,11 @@ int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len, > QTAILQ_INSERT_TAIL(&cpu->watchpoints, wp, entry); > } > > - tlb_flush_page(cpu, addr); > + if (((addr + len) & TARGET_PAGE_MASK) != (addr & TARGET_PAGE_MASK)) { This computation will be false when adding a watchpoint for the last len bytes in the page, and no actual page crossing is required. For this reason I prefer in_page = -(addr | TARGET_PAGE_MASK); if (len <= in_page) r~ > + tlb_flush(cpu); > + } else { > + tlb_flush_page(cpu, addr); > + } > > if (watchpoint) > *watchpoint = wp; >
diff --git a/exec.c b/exec.c index 5162f0d12f9..851ac180fe7 100644 --- a/exec.c +++ b/exec.c @@ -1056,7 +1056,11 @@ int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len, QTAILQ_INSERT_TAIL(&cpu->watchpoints, wp, entry); } - tlb_flush_page(cpu, addr); + if (((addr + len) & TARGET_PAGE_MASK) != (addr & TARGET_PAGE_MASK)) { + tlb_flush(cpu); + } else { + tlb_flush_page(cpu, addr); + } if (watchpoint) *watchpoint = wp;
There is no particular reason why you can't have a watchpoint in TCG that covers a large chunk of the address space. We could be clever about it but these cases are pretty rare and we can assume the user will expect a little performance degradation. NB: In my testing gdb will silently squash a watchpoint like: watch (char[0x7fffffffff]) *0x0 to a 4 byte watchpoint. Practically it will limit the maximum size based on max-value-size. However given enough of a tweak the sky is the limit. Reported-by: Alexander Bulekov <alxndr@bu.edu> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> --- exec.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) -- 2.20.1