This reminds me that the GET_ set stuff should treat the variables as volatile, because otherwise if it can be changed from outside compiler might not know and will happily perform a test on register version of the variable. Or even better, it should contain memory clobber asm volatile ("" ::: "memory") which will act as a barrier for compiler to reload all variables used and not rely on cached values in registers.
Just to make it more clear, this remark is just for the situation if you may have irq handler interrupting a function. Compiler can read from memory just once and use cached value in register.
All in all everything depends what can/could be called while interrupts are enabled in seabios. If you want to have the GET/SET stuff at least atomic, and reloadable then use same thing as in Linux kernel "atomic" variables. On x86 mov is guaranteed to be atomic (at most 32bit only) and because it is internally implemented as structure with volatile property it works fine in all cases.
In my case I use here 64bit data then it means I need to use irq_save restore in any case. It is even doing a barrier for compiler. Therefore I think it is the best solution here.